Method of handoff within a telecommunications system containing digital base stations with different spectral capabilities

ABSTRACT

The present invention is directed to a digital wireless telecommunications system that includes a plurality of base station of differing spectral capabilities, and a plurality of remote stations capable of transmitting data to and receiving transmissions from the plurality of base stations. The invention herein provides a method for remote station hand-off between base stations of a narrower spectral capacity and base stations of a wider spectral capacity. A method is provided for a wireless telecommunications infrastructure to facilitate a remote station hand-off from a set of narrowband compliant base stations to at least one wideband compliant base station while a remote station is in the coverage area of both types of base stations. Additionally, the invention herein provides remote station apparatus, base station apparatus, and base station controller apparatus for performing the handoff methodology of the present invention.

CLAIM OF PRIORITY UNDER 35; U.S.C. §120

The present Application for Patent is a Continuation of U.S. patentapplication Ser. No. 10/969,638, entitled “METHOD OF HANDOFF WITHIN ATELECOMMUNICATIONS SYSTEM CONTAINING DIGITAL BASE STATIONS WITHDIFFERENT SPECTRAL CAPABILITIES” filed Oct. 20, 2004, now U.S. Pat. No.7,151,933, which is a Continuation of U.S. patent application Ser. No.10/213,601, entitled METHOD OF HANDOFF WITHIN A TELECOMMUNICATIONSSYSTEM CONTAINING DIGITAL BASE STATIONS WITH DIFFERENT SPECTRALCAPABILITIES” filed Aug. 6, 2002, now U.S. Pat. No. 6,853,843, which isa Continuation and claims priority to U.S. patent application Ser. No.09/546,219, entitled “METHOD OF HANDOFF WITHIN A TELECOMMUNICATIONSSYSTEM CONTAINING DIGITAL BASE STATIONS WITH DIFFERENT SPECTRALCAPABILITIES” filed Apr. 7, 2000 now U.S. Pat. No. 6,535,739, andassigned to the assignee hereof and hereby expressly incorporated byreference herein.

BACKGROUND

1. Field

The present invention relates to wireless telecommunications. Moreparticularly, the present invention relates to a novel method forfacilitating handoffs between digital base stations with differentspectral capabilities.

2. Background

In a code division multiple access (CDMA) spread spectrum communicationsystem, a common frequency band is used for communication with all basestations within that system. An example of such a system is described inthe TIA/EIA Interim Standard IS-95-A entitled “Mobile Station-BaseStation Compatibility Standard for Dual-Mode Wideband Spread SpectrumCellular System”, incorporated herein by reference. The generation andreceipt of CDMA signals is disclosed in U.S. Pat. No. 4,901,307 entitled“SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEMS USING SATELLITEOR TERRESTRIAL REPEATERS” and in U.S. Pat. No. 5,103,459 entitled“SYSTEM AND METHOD FOR GENERATING WAVEFORMS IN A CDMA CELLULAR TELEPHONESYSTEM” both of which are assigned to the assignee of the presentinvention and incorporated herein by reference.

Signals occupying the common frequency band are discriminated at thereceiving station through the spread spectrum CDMA waveform propertiesbased on the use of a high rate pseudonoise (PN) code. A PN code is usedto modulate signals transmitted from the base stations and the remotestations. Signals from different base stations can be separatelyreceived at the receiving station by discrimination of the unique timeoffset that is introduced in the PN codes assigned to each base station.The high rate PN modulation also allows the receiving station to receivea signal from a single transmission station where the signal hastraveled over distinct propagation paths. Demodulation of multiplesignals is disclosed in U.S. Pat. No. 5,490,165 entitled “DEMODULATIONELEMENT ASSIGNMENT IN A SYSTEM CAPABLE OF RECEIVING MULTIPLE SIGNALS”and in U.S. Pat. No. 5,109,390 entitled “DIVERSITY RECEIVER IN A CDMACELLULAR TELEPHONE SYSTEM”, both of which are assigned to the assigneeof the present invention and incorporated herein by reference.

U.S. Pat. No. 5,101,501 entitled “METHOD AND SYSTEM FOR PROVIDING A SOFTHANDOFF IN A CDMA CELLULAR TELEPHONE SYSTEM,” and U.S. Pat. No.5,267,261 entitled “MOBILE STATION ASSISTED SOFT HANDOFF IN A CDMACELLULAR COMMUNICATIONS SYSTEM,” both of which are assigned to theassignee of the present invention and are incorporated herein byreference, disclose a method and system for simultaneous communicationbetween a remote station and more than one base station, known as softhandoff. Further information concerning handoff is disclosed in U.S.Pat. No. 5,101,501, entitled “METHOD AND SYSTEM FOR PROVIDING A SOFTHANDOFF IN COMMUNICATIONS IN A CDMA CELLULAR TELEPHONE SYSTEM”, U.S.Pat. No. 5,640,414, entitled “MOBILE STATION ASSISTED SOFT HANDOFF IN ACDMA CELLULAR COMMUNICATIONS SYSTEM”, and U.S. Pat. No. 5,625,876entitled “METHOD AND APPARATUS FOR PERFORMING HANDOFF BETWEEN SECTORS OFA COMMON BASE STATION,” each of which is assigned to the assignee of thepresent invention and incorporated in its entirety herein by thisreference. The subject matter of U.S. Pat. No. 5,625,876 concerns whatis known in the art as “softer handoff.” For the purposes of thisdocument, the term “soft handoff” is intended to include both “softhandoff” and “softer handoff.”

If a remote station travels outside the boundary of the system withwhich it is currently communicating, it is desirable to maintain thecommunication link by transferring the call to a neighboring system, ifone exists. The neighboring system may use any wireless technology,examples of which are CDMA, NAMPS, AMPS, TDMA or FDMA. If theneighboring system uses CDMA on the same frequency band as the currentsystem, an inter-system soft handoff can be performed. In situationswhere inter-system soft handoff is not available, the communication linkis transferred through a hard handoff where the current connection isbroken before a new one is made. Examples of hard handoffs are thosefrom a CDMA system to a system employing an alternate technology or acall transferred between two CDMA systems which use different frequencybands (inter-frequency hard handoff).

Inter-frequency hard handoffs can also occur within a CDMA system. Forexample, a region of high demand such as a downtown area may require agreater number of frequencies to service demand than the suburban regionsurrounding it. It may not be cost effective to deploy all availablefrequencies throughout the system. A call originating on a frequencydeployed only in the high congestion area must be handed off as the usertravels to a less congested area. Another example is that of a microwaveor other service operating on a frequency within the system'sboundaries. As users travel into an area suffering from interferencefrom the other service, their call may need to be handed off to adifferent frequency.

Handoffs can be initiated using a variety of techniques. Handofftechniques, including those using signal quality measurements toinitiate handoff, are found in U.S. Pat. No. 5,697,055 entitled “METHODAND APPARATUS FOR HANDOFF BETWEEN DIFFERENT CELLULAR COMMUNICATIONSSYSTEMS”, issued Dec. 09, 1997, assigned to the assignee of the presentinvention and incorporated herein by reference. Further disclosure onhandoffs, including measurement of round-trip signal delay to initiatehandoff, is disclosed in U.S. Pat. No. 5,848,063, entitled “METHOD ANDAPPARATUS FOR HARD HANDOFF IN A CDMA SYSTEM”, issued Dec. 8, 1998,assigned to the assignee of the present invention and incorporatedherein by reference. Handoffs from CDMA systems to alternate technologysystems are disclosed in U.S. Pat. No. 5,594,718 ('306 application)entitled “METHOD AND APPARATUS FOR MOBILE UNIT ASSISTED CDMA TOALTERNATIVE SYSTEM HARD HANDOFF”, issued Jan. 14, 1997, assigned to theassignee of the present invention and incorporated herein by reference.In the '306 application, pilot beacons are placed at the boundaries ofthe system. When a remote station reports these pilots to the basestation, the base station knows that the remote station is approachingthe boundary.

When a system has determined that a call should be transferred toanother system via hard handoff, a message is sent to the remote stationdirecting it to do so along with parameters that enable the remotestation to connect with the destination system. The system has onlyestimates of the remote station's actual location and environment, sothe parameters sent to the remote station are not guaranteed to beaccurate. For example, with beacon aided handoff, the measurement of thepilot beacon's signal strength can be a valid criterion for triggeringthe handoff. However, the appropriate cell or cells in the destinationsystem which are to be assigned to the remote station (known as theActive Set) are not necessarily known.

The cdma2000 cellular telephone standard proposal issued by theTelecommunications Industry Association (TIA), entitled “cdma2000 SeriesTIA/EIA/IS-2000,” published in August of 1999, hereinafter referred toas cdma2000, uses advanced signal processing techniques to provideefficient and high quality phone service, and is incorporated herein byreference. For example, a cdma2000 compliant cellular telephone systemutilizes decoding, error detection, forward error correction (FEC),interleaving, and spread spectrum modulation in order to make moreefficient use of the available radio frequency (RF) bandwidth, and toprovide robust connections. In general, the benefits provided bycdma2000 include longer talk time and fewer dropped calls when comparedto other types of cellular telephone systems.

In the world of cellular telecommunications, those skilled in the artoften use the terms 1G, 2G, and 3G. The terms refer to the generation ofthe cellular technology used. 1G refers to the first generation, 2G tothe second generation, and 3G to the third generation. 1G is used torefer to the analog phone system, known as an AMPS (Advanced MobilePhone Service) phone systems.

2G is commonly used to refer to the digital cellular systems that areprevalent throughout the world, and include cdmaOne, Global System forMobile communications (GSM), and Time Division Multiple Access (TDMA).cdmaOne, based on a Code Division Multiple Access (CDMA) technology,refers to a digital cellular system that adheres to the family of IS-95standards. 2G systems can support a greater number of users in a densearea than can 1G systems.

3G is commonly used to refer to the digital cellular systems currentlybeing developed. 3G systems include cdma2000 and Wideband-CDMA (W-CDMA).3G systems promise higher peak data transfer rates than do their 2Gcounterparts. Additionally, many 3G systems can support a greater numberof users than can 2G systems.

Spreading Rate 3 versions of cdma2000, hereinafter referred to as 3x,use a frequency band of 3.75 megahertz (MHz), comprised of three 1.25MHz chunks, while the Spreading Rate 1 versions of cmda2000, hereinafterreferred to as 1X, uses a frequency band having a width of 1.25 MHz.Wherein 1X is a single carrier protocol, 3X is a multi-carrier protocol.As would be known to one skilled in the art, a single carrier protocoltransmits data in a single frequency band, while a multi-carrierprotocol, transmits data in multiple [single carrier] frequency bands.For instance, whereas 1X transmits data in a single 1.25 MHz frequencybands, 3X transmits data in three 1.25 MHz frequency bands. Themodulation techniques performed by multi-carrier systems, hereinafterreferred to as a multi-carrier modulation techniques, differ from thoseperformed by single carrier systems, hereinafter referred to as singlecarrier modulation techniques. Although the examples of 1X and 3X areused as single carrier and multi-carrier protocols respectively, theinvention is not limited to 1X and 3X protocols, and applies equallywell to any system that is comprised of both single carrier andmulti-carrier base stations, such as may be the case in future versionsof W-CDMA that are attempting to support higher data transmission rates.

Any given cdma2000 system need not support 1x (version 1X of cdma2000)exclusively or 3X (version 3X of cdma2000) exclusively. A version ofcdma2000 that uses a multi-carrier 3.75 MHz spectrum on the forwardlink, the wireless link that delivers data from the base station to theremote station, but uses a single carrier 1.25 MHz spectrum on thereverse link, the wireless link that delivers data from the remotestation to the base station is described in U.S. patent application Ser.No. 09/382,438 entitled “Method and Apparatus Using a Multi-CarrierForward Link in a Wireless Communication System” assigned to theassignee of the present invention and incorporated herein by reference.A system such as this, that uses multi-carrier capabilities on theforward link, but uses single carrier capabilities on the reverse link,is hereinafter referred to as a hybrid system. A 3X/1X system is merelyused as an example, and a hybrid system is not limited to such anembodiment. A block diagram of an exemplary hybrid system is shown inFIG. 1.

FIG. 1 is a block diagram of an exemplary simplified cellular telephonesystem that uses multi-carrier transmission on the forward link andsingle carrier transmissions on the reverse link, wherein a 3X protocolis used on the forward link and a 1X protocol is used on the reverselink. Remote stations such as remote stations 110 (typically cellulartelephones, personal digital assistants (PDAs) with wirelesscapabilities, or laptop computers with wireless capabilities) arelocated among base stations 120. The remote stations 110 a and 110 b arein an active mode and are therefore interfacing with at least one basestation 120 using radio frequency (RF) signals modulated in accordancewith the CDMA signal processing techniques. A system and method formodulating RF signals in accordance with CDMA modulation is described inU.S. Pat. No. 5,103,459 entitled “System and Method for GeneratingSignal Waveforms in a CDMA Cellular Telephone System” assigned to theassignee of the present invention and previously incorporated herein byreference. The other remote stations 110 are in standby mode and aretherefore monitoring either a full paging channel for page messagesindicating a request to communicate, or they are monitoring a quickpaging channel for indicator bits indicating whether a message isexpected on a full paging channel.

Each given base station 120 that is in active mode with at least oneremote station 110 transmits data to remote stations 110 across threefrequency bands f1, f2, f3, and receives data from remote stations 110in a single frequency band f4. Each frequency band f1, f2, f3, and f4has the same bandwidth. Frequency bands f1, f2, and f3 are adjacentfrequency bands. For instance, if in the example of the hybrid systemeach band f1 was the frequency band 1900 MHz-1901.25 MHz, then f2 wouldbe 1901.25 MHz-1902.5 MHz, and f3 would be 1902.5 MHz-1903.75 MHz. Thus,the adjacent frequency bands take up the spectrum 1900 MHz-1903.75 MHzin this example. In such a case, f4 would be a 1.25 MHz band locatedoutside of that frequency range. For example, f4 could be located at1820 MHz-1821.25 MHz.

Base stations 120 connect to a Base Station Controller (BSC) 114. BaseStation Controller 114 controls base stations 120, and exchangesinformation packets between Mobile Switching Center (MSC) 116 and basestations 120. Mobile Switching Center 116 exchanges information packetsbetween Public Switched Telephone Network 118. In other embodiments,different switches, such as a packet data serving node (PDSN), can beconnected to the system. A cellular telephone system can contain morethan one Base Station Controller 114 and more than one Mobile SwitchingCenter 116, or conversely, in decentralized systems, such as thosedisclosed in U.S. Pat. No. 6,215,779, entitled “DISTRIBUTEDINFRASTRUCTURE FOR WIRELESS DATA COMMUNICATIONS”, issued Apr. 10, 2001,assigned to the assignee of the present invention, and incorporated byreference herein, Base Station Controller 114 or Mobile Switching Center116 may be absent from the cellular telephone system.

FIG. 2 is a block diagram of an exemplary simplified cellular telephonesystem that uses single carrier transmissions on the forward link andsingle carrier transmissions on the reverse link. Remote stations suchas remote stations 210 (typically cellular telephones) are located amongbase stations 220. The remote stations 210 a and 210 b are in an activemode and are therefore interfacing with at least one base station 220using radio frequency (RF) signals modulated in accordance with the CDMAsignal processing techniques. The other remote stations 210 are instandby mode and are therefore monitoring either a full paging channelfor page messages indicating a request to communicate, or they aremonitoring a quick paging channel for indicator bits indicating whethera message is expected on a full paging channel.

Each given base station 220 that is in active mode with at least oneremote station 210, transmits data to remote stations 210 across asingle frequency band f1, and receives data from remote stations 210 ina single frequency band f2. Each frequency band f1 and f2 has the samebandwidth. Frequency bands f1 and f2 can be offset by a predefinedamount. If an amount of 80 MHz is used, and f1 is at the frequency band1900 MHz-1901.25 MHz, then f2 could be located at 1820.00 MHz-1821.80 25MHz.

Base stations 220 connect to a Base Station Controller 114. Base StationController 114 controls base stations 220, and exchanges informationpackets between Mobile Switching Center 116 and base stations 220.Mobile Switching Center 116 exchanges information packets between PublicSwitched Telephone Network 118. In other embodiments, differentswitches, such as a packet data serving node (PDSN), can be connected tothe system. A cellular telephone system can contain more than one BaseStation Controller 114 and more than one Mobile Switching Center 116, orconversely, in decentralized systems, such as those disclosed in U.S.Pat. No. 6,215,779 entitled “DISTRIBUTED INFRASTRUCTURE FOR WIRELESSDATA COMMUNICATIONS”, issued Apr. 10, 2001, applied for by the applicantof the present invention, and incorporated by reference herein, BaseStation Controller 114 or Mobile Switching Center 116 may be absent fromthe cellular telephone system as separate entities, but rather may beintegrated into the base stations themselves.

FIG. 3 is a block diagram of an exemplary simplified cellular telephonesystem that uses multi-carrier transmissions on the forward link andmulti-carrier transmissions on the reverse link. Remote stations such asremote stations 310 (typically cellular telephones) are located amongbase stations 320. The remote stations 310 a and 310 b are in an activemode and are therefore interfacing with at least one base station 320using radio frequency (RF) signals modulated in accordance with the CDMAsignal processing techniques. The other remote stations 310 are instandby mode and are therefore monitoring either a full paging channelfor page messages indicating a request to communicate, or they aremonitoring a quick paging channel for indicator bits indicating whethera message is expected on a full paging channel.

Each given base station 320 that is in active mode with at least oneremote station 310, transmits data to remote stations 310 across threefrequency bands, f1, f2, f3, and receives data from remote stations 310across three frequency bands f4, f5, f6. Each frequency band f1, f2, 3,f4, f5, f6 has the same bandwidth. Frequency bands f1, f2, and f3 areadjacent frequency bands. For instance, if in the example of the hybridsystem each band f1 was the frequency band 1900 MHz-1901.25 MHz, then f2would be 1901.25 MHz-1902.5 MHz, and f3 would be 1902.5 MHz-1903.75 MHz.Thus the adjacent frequency bands take up the spectrum 1900 MHz-1903.75MHz in this example. Likewise, frequency bands f4, f5, and f6 areadjacent to one another. Frequency bands f1 and f4 can be offset by apredefined amount. If an amount of 80 MHz is used, and f1 begins at thefrequency 1900 MHz, then reverse link bands f4, f5, f6, could take upthe 3.75 MHz spectrum located between 1820 MHz-1823.75 MHz.

Although a carrier could upgrade its entire network from a singlecarrier system to a multi-carrier system all at once, this is oftenundesirable in light of costs. Economically, it may be more desirablefor a carrier to put multi-carrier capabilities in a few areas of theirnetwork that will benefit the most from multi-carrier capabilities, andthen slowly roll out multi-carrier capabilities into other areas of itsnetwork over time. During such a gradual rollout, some of the basestations in the system will be multi-carrier protocol compliant whileothers will not. Likewise, some carriers may find it desirable toupgrade a portion of its network to support a multi-carrier protocol,without having the intent of ever upgrading the remaining portion of itsnetwork to a multi-carrier protocol.

What is needed is a method and apparatus for performing handoff in awireless telecommunication system that contains digital base stations,some of which comply with a multi-carrier protocol and some of which arenot multi-carrier compliant.

SUMMARY

The present invention is directed to a digital wirelesstelecommunications system that includes a plurality of base stations ofdiffering spectral capabilities, and a plurality of remote stationscapable of transmitting data to and receiving transmissions from theplurality of base stations. The invention herein provides a method forremote station handoff between base stations of a narrower spectralcapacity and base stations of a wider spectral capacity. A method isprovided for a wireless telecommunications infrastructure to facilitatea remote station hand-off from a set of single carrier compliant basestations to at least one multi-carrier compliant base station while aremote station is in the coverage area of both types of base stations.

In one embodiment the handoff is enabled by transmitting a message to aremote station that indicates that the remote station should transmitmodulated signals according to a single carrier protocol (e.g., 1X) andshould receive modulated signals according to a multi-carrier protocol.In another embodiment, the remote station is instructed to transmit themodulated signals in the same frequency band as was used fortransmission prior to the handoff. In another embodiment, the remotestation is instructed to transmit the modulated signals in a differentfrequency band than was used for transmission prior to the handoff. Inanother embodiment the single carrier compliant base stations transmitin the single carrier frequency a portion of the signal that isgenerated in accordance with the multi-carrier protocol.

In another embodiment, the handoff is enabled by transmitting a messageto a remote station that indicates that the remote station shouldtransmit modulated signals according to a multi-carrier protocol andshould receive modulated signals according to a multi-carrier protocol.

In another embodiment, the handoff is enabled by transmitting a messageto a remote station that indicates that the remote station shouldtransmit modulated signals according to a single carrier protocol andshould receive modulated signals according to a single carrier protocol.In this embodiment, the remote station is instructed that it shouldreceive single carrier modulated signals from at least one multi-carriercompliant base station.

In many of the embodiments, a means to avoid reverse link interferenceis achieved by performing a two part handoff, the first of which isperformed while the remote station is in the coverage of both types ofbase stations, and the second of which occurs when the remote stationtravels to an area that is only in the coverage of multi-carriercompliant base stations.

The remote station adjusts its transmit and receive modulationtechniques in accordance with the received handoff messages of the aboveembodiments.

The invention herein also provides remote station apparatus, basestation apparatus, and base station controller apparatus for performingthe above-described methodology.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, objects, and advantages of the present invention willbecome more apparent from the detailed description set forth below whentaken in conjunction with the drawings in which like referencecharacters identify like features correspondingly throughout:

FIG. 1 is a block diagram of an exemplary simplified cellular telephonesystem that uses multi-carrier transmissions on the forward link andsingle carrier transmissions on the reverse link, wherein a 3X protocolis used on the forward link and a 1X protocol is used on the reverselink.

FIG. 2 is a block diagram of an exemplary simplified cellular telephonesystem that uses single carrier transmissions on the forward link andsingle carrier transmissions on the reverse link.

FIG. 3 is a block diagram of an exemplary simplified cellular telephonesystem that uses multi-carrier transmissions on the forward link andmulti-carrier transmissions on the reverse link.

FIG. 4 is a simplified network diagram of an exemplary embodiment of thecoverage of a spread spectrum system in the midst of a hybrid deploymentof single carrier services to multi-carrier services.

FIG. 5 diagrams a portion of the simplified network diagram of FIG. 4,and also shows the path of an exemplary remote station travelingthroughout the network.

FIG. 6 is an exemplary diagram of the communication path of a remotestation that is a multi-carrier handoff candidate communicating with twosingle carrier base stations BS1.

FIG. 7 is a diagram of an exemplary communication path during thehandoff of a first handoff embodiment.

FIG. 8 is a diagram of an exemplary communication path during thehandoff of a second handoff embodiment.

FIGS. 9 a and 9 b contain an illustration of the spectral density andthe associated transmission power that would be utilized to transmit Ninformation bits using an exemplary single carrier protocol.

FIG. 10 a contains an illustration of the spectral density and theassociated transmission power that would be utilized in a firstembodiment to simultaneously transmit N information bits using anexemplary single carrier protocol and transmit N information bits usingan exemplary multi-carrier protocol.

FIG. 10 b contains an illustration of the spectral density and theassociated transmission power that would be utilized in a secondembodiment to simultaneously transmit N information bits using anexemplary single carrier protocol and transmit N information bits usingan exemplary multi-carrier protocol.

FIG. 11 contains an illustration of the spectral density and theassociated forward link transmission power that would be utilized totransmit N information bits using an exemplary multi-carrier protocol.

FIG. 12 contains an illustration of the spectral density and theassociated forward link transmission power that would be utilized in afirst embodiment to simultaneously transmit N information bits using anexemplary single carrier protocol and transmit N information bits usingan exemplary multi-carrier protocol.

FIG. 13 is a diagram of an exemplary communication path during thehandoff of a third handoff embodiment.

FIG. 14 contains an exemplary illustration of the spectral density andthe associated forward link transmission power that would be utilized totransmit N information bits to two remote stations using an exemplarymulti-carrier protocol to communicate with each remote station.

FIG. 15 is a diagram of an exemplary communication path during thehandoff of a fourth handoff embodiment.

FIG. 16 is a diagram of an exemplary communication path during thehandoff of a fifth handoff embodiment.

FIG. 17 a contains an exemplary illustration of a transmittedmulti-carrier signal.

FIG. 17 b contains an exemplary illustration of a portion of themulti-carrier signal shown in FIG. 17 a that can be transmitted in asingle carrier frequency band.

FIG. 18 is a diagram of an exemplary communication path during thehandoff of a sixth handoff embodiment.

FIG. 19 is a diagram of an exemplary communication path during thehandoff of a seventh handoff embodiment.

FIG. 20 is a diagram of an exemplary communication path during thehandoff of an eighth handoff embodiment.

FIG. 21 is a flowchart of the methodology that can be used to implementthe first through the eighth handoff embodiments.

FIG. 22. is an exemplary block diagram of a base station apparatus thatcan be used to perform the first through the eight handoff embodiments.

FIG. 23. is an exemplary block diagram of a remote station apparatusthat can be used to perform the first through the eight handoffembodiments.

FIG. 24. is an exemplary block diagram of a base station controller(BSC) apparatus that can be used to perform the first through the eighthandoff embodiments.

DETAILED DESCRIPTION

Although many of the detailed descriptions are discussed in reference toa cdma2000 system containing 1X and 3X base stations, one skilled in theart will appreciate that the invention can be applied to any spreadspectrum system and is not limited to the 1X and 3X systems used in manyof the exemplary embodiments.

When discussing signal transmissions in a frequency range, the phrase‘in a frequency band’ is used herein to refer to a spread spectrumsignal that is spread across a given frequency. For instance, whenstating that a signal is transmitted in frequency band X, whereinfrequency band X is defined as the band ranging from 1900 MHz-1903.75MHz, it is meant that the transmitted signal is spread across thefrequency band 1900 MHz-1903.75 MHz.

FIG. 4 is a simplified network diagram of an exemplary embodiment of thecoverage of a spread spectrum system in the midst of a hybrid deploymentof single carrier services to multi-carrier services.

In the network diagram, each circular footprint labeled BS3 represents abase station that is multi-carrier compliant and its correspondingcoverage/footprint. Each circle, itself, is representative of thefootprint of a base station BS3. Although the physical base station,BS3, is not diagrammed separately within the figure, it can be assumedthat it lays somewhere within the diagrammed footprint. Eachmulti-carrier compliant base station is capable of both transmitting andreceiving spread spectrum signals in accordance with a multi-carrierprotocol. Hereinafter, all multi-carrier compliant base stations willsimply be referred to as multi-carrier base stations.

In the network diagram, each circular footprint labeled BS1 represents abase station that is single carrier compliant and its correspondingcoverage/footprint. Each circle, itself, is representative of thefootprint of a base station BS1. Although the physical base station,BS1, is not diagrammed separately within the figure, it can be assumedthat it lays somewhere within the diagrammed footprint. Each singlecarrier compliant base station is capable of both transmitting andreceiving spread spectrum signals in accordance with a single carrierprotocol (e.g., 1X). Hereinafter, all single carrier compliant basestations will simply be referred to as single carrier base stations.

A carrier (e.g. Vodafone AirTouch) will likely deploy multi-carrierservices in small areas, or pockets, wherein multi-carrier services arefirst needed. FIG. 4 illustrates an example of such a network 410,wherein a small pocket of multi-carrier services is provided by sixmulti-carrier base stations, BS3, and wherein single carrier servicesare provided in a large surrounding area by forty-eight single carrierbase stations, BS1. Hereinafter, the term non-homogenous network will beused to refer to a network containing both multi-carrier base stationsand single carrier base stations, such as network 410. Thenon-homogenous network is essentially the combination of a singlecarrier system (the base stations labeled BS1) and a multi-carriersystem (the base stations labeled BS3) that share common infrastructure,such as a BSC or MSC.

Multi-carrier base stations BS3 are not necessarily limited tocommunicating with remote stations by transmitting data to a remotestation in compliance with a multi-carrier protocol in a multi-carrierfrequency band. Rather, though, multi-carrier base stations BS3 may alsobe able to communicate with remote stations in accordance with a singlecarrier protocol in a single carrier frequency.

Having such flexibility in multi-carrier base stations proves usefulwhen a network 410 is created by upgrading a pocket of single carrierbase stations to multi-carrier base stations. In such a network 410,many pre-existing remote stations that desire service on the network 410may only be single carrier compliant. So as not to deny service tonon-multi-carrier compliant remote stations that have traveled intothese upgraded pockets, the upgraded base stations may continue toprovide single carrier compliant services in addition to the newly addedmulti-carrier services.

Although a multi-carrier base station, as used herein, can mean a basestation that is not only multi-carrier compliant, but one thatadditionally is single carrier compliant, the same does not hold truefor the meaning of a single carrier base station. A single carrier basestation, as used herein, is a base station that is single carriercompliant and is not fully multi-carrier compliant. Thus, single carrierbase stations cannot both transmit data on a multi-carrier forward linkin accordance with a multi-carrier protocol and receive data on amulti-carrier reverse link in accordance with a multi-carrier protocol.All base stations that can both transmit data on a multi-carrier forwardlink in accordance with a multi-carrier protocol and receive data on amulti-carrier reverse link in accordance with a multi-carrier protocolare referred to herein as multi-carrier base stations.

FIG. 5 diagrams a portion of the network 410, and also shows the path ofan exemplary remote station traveling throughout the network. Subscriptshave been added to each instance of BS1 and BS3 for distinguishmentpurposes.

In FIG. 5, a remote station is in a call while traveling throughout aportion of network 410. The remote station begins its call at point 510and terminates its call at point 558. “X”es are placed in the diagram tocall to the attention of the reader various points at which the remotestation is in different coverage areas.

At points 510 through 518, the remote station is solely in the coverageareas of single carrier base stations. At point 510, the remote stationis only in the coverage area of BS1 a. At point 518, the remote stationis in the coverage area of both BS1 d and BS1 e. Because the remotestation never enters multi-carrier coverage between these points, nohandoff is needed between the multi-carrier base stations and the singlecarrier base stations.

At points 530 through 538, the remote station is solely in the coveragearea of multi-carrier base stations. At point 530, the remote station isonly in the coverage area of BS3 c. At point 538, the remote station isin the coverage area of BS3 f. Because the remote station never enterssingle carrier coverage between these points, no handoff is neededbetween the multi-carrier base stations and the single carrier basestations between these points.

At points 550 through 558, the remote station is solely in the coverageareas of single carrier base stations. At point 550, the remote stationis only in the coverage area of BS1 h. At point 558, the remote stationis in the coverage area of BS1 k. Because the remote station neverenters multi-carrier coverage between these points, no handoff is neededbetween the multi-carrier base stations and the single carrier basestations, between these points.

At points 520 through 528, the remote station is within the coverageareas of both single carrier base stations and multi-carrier basestations. At point 520, the remote station is in the coverage area ofsingle carrier base stations BS1 d and BS1 e, and it is also in thecoverage area of multi-carrier base station BS3 b. At point 528, theremote station is in the coverage area of single carrier base stationBS1 f, and it is also in the coverage area of multi-carrier base stationBS3 c.

At points 540 through 548, the remote station is within the coverageareas of both single carrier base stations and multi-carrier basestations. At point 540, the remote station is in the coverage area ofsingle carrier base stations BS1 i, and it is also in the coverage areaof multi-carrier base station BS3 f. At point 548, the remote station isin the coverage area of single carrier base stations BS1 h and BS1 i,and it is also in the coverage area of multi-carrier base station BS3 e.

In order to keep the call up, at some point between point 518 and point530 a handoff must occur between single carrier base stations BS1 andmulti-carrier base stations BS3. Likewise, at some point between point538 and point 550 a handoff must occur between multi-carrier basestations BS3 and single carrier base stations BS1.

Several embodiments of the invention facilitate such a handoff. Somenotation will prove helpful in describing these embodiments. Nf will beused hereinafter to represent a particular single carrier frequency band(such as 1900 MHz-1901.25 MHz) used for the forward link, while Nr willbe used hereinafter to represent a particular single carrier frequencyused for the reverse link. The term multi-carrier frequency band ishereinafter used to refer to the set of single-carrier frequency bandsused for a multi-carrier transmission. For instance, if the combinationof transmissions on frequency bands 1900-1901.25 MHz, 1901.25-1902.50MHz, and 1902.50-1903.75 MHz is used to send a multi-carrier signal(e.g. a 3X transmission signal), then the set of these single-carrierfrequency bands comprises a multi-carrier frequency band. Wf will beused hereinafter to represent a particular multi-carrier frequency bandused for the forward link, while Wr will be used hereinafter torepresent a particular multi-carrier frequency band used for the reverselink. Nf can be contained within Wf, or it can be a frequency bandoutside of Wf, further discussed in reference to FIG. 7. Likewise, Nrcan be contained within Wr, or it can be a frequency band outside of Wr.

A remote station that is communicating with at least one base stationBS1 via a single carrier protocol on frequencies Nf and Nr, while it isalso in the coverage area of at least one multi-carrier base stationBS3, is hereinafter referred to as a multi-carrier handoff candidate.Referring to FIG. 5, if the remote station is only communicating withBS1 d and BS1 e at point 520, it would be considered a multi-carrierhandoff candidate at that point, since it is also in the coverage areaof a multi-carrier base station BS3 b. It should be noted that point 520is not the only spot at which the remote station could be considered amulti-carrier handoff candidate. At all points 520-528, if the remotestation is communicating with at least one single carrier base stationBS1, but it is not communicating with any multi-carrier base stationsBS3, the remote station would be considered a multi-carrier handoffcandidate.

Multiple embodiments of the invention, each for facilitating a handoffin a non-homogenous system, are described below. Following thedescription of these embodiments is a description of a flow chart thatcan be used for all handoff embodiments.

In a first handoff embodiment of the present invention, a multi-carrierhandoff candidate is sent a handoff message (often referred to as anextended handoff direction message) from at least one single carrierbase station BS1, instructing it to cease single carrier communicationswith single carrier base stations BS1 on Nf and Nr, and to beginmulti-carrier communications on frequencies Wf and Wr with multi-carrierbase stations BS3. For instance, at point 520, the remote station, whichwas communicating with BS1 d and BS1 e on frequencies Nf and Nr using asingle carrier protocol, would be instructed to switch its mode ofcommunication to a multi-carrier protocol on frequencies Wf and Wr, andto only communicate with base station BS3 b. In such an embodiment, theinfrastructure instructs the multi-carrier base stations BS3 to begincommunications with the remote station using the multi-carrier protocolon frequencies Wf and Wr. The infrastructure also instructs the singlecarrier base stations BS1 to cease communications with the remotestation. Using point 520 as an exemplary point of handoff, figures usedherein will assume a multi-carrier handoff candidate that is in thecoverage area of two single carrier base stations BS1 and onemulti-carrier base station BS3. However, one skilled in the art willrealize that a multi-carrier handoff candidate could be in a coveragearea in which there are more or less of either type of base station, aslong as it is in the coverage area of at least one single carrier basestation and one multi-carrier base station. One skilled in the art willalso appreciate that the descriptions of the below embodiments are notlimited to coverage areas of exactly two single carrier base stationsBS1 and one multi-carrier base station BS3, but that they apply to othercoverage mixes as well, such as a point that is in the coverage area oftwo multi-carrier base stations BS3 and only one single carrier basestation BS1.

An exemplary diagram of the communication path of a remote station thatis a multi-carrier handoff candidate communicating with two singlecarrier base stations BS1 is shown in FIG. 6. A diagram of an exemplarycommunication path after the handoff of a first handoff embodimentappears in FIG. 7, wherein the remote station begins transmitting infrequency band Wr, and begins receiving in frequency band Wf, andwherein transmissions adhering to the multi-carrier protocol arereceived by a base station BS3, and wherein the base station BS3 beginstransmitting in accordance with the multi-carrier protocol in frequencyband Wf.

Although this first handoff embodiment succeeds in allowing a remotestation to keep up a communications link while traveling throughout anon-homogenous network, it lacks the desirable features of communicationpath diversity and power control that can be provided by soft handoff.

The lack of being in communication with both single carrier basestations and multi-carrier base stations when in the coverage of bothnegatively affects path diversity. If the remote station performs ahandoff of the first handoff embodiment just prior to point 520, thenthe remote station will only have communication links established withmulti-carrier base station BS3 b. Although the remote station is in thecoverage areas of both BS1 d and BS1 e, it will no longer havecommunication links with these base stations, and will not gain the pathdiversity that could have been received by being in a soft handoff withthese base stations. This is especially evident in instances where Nf iscontained within Wf, and where BS1 d or BS1 e is transmitting at aparticularly high power level and is interfering with the signalstransmitted from BS3 b. If the remote station had been in soft handoffwith BS3 b, BS1 d, and BS1 e, it would likely have received a goodtransmission from the high powered base station, either BS1 d or BS1 e,whose high transmission power level significantly corrupted thetransmission signal transmitted by BS3 b. However, in the case that itis not in such a soft handoff, as is the case in the first handoffembodiment, it would only receive the corrupted signal from BS3 b.

The lack of such a soft handoff negatively affects reverse link powercontrol as well. For instance, if after a handoff of the first handoffembodiment, at point 520 BS3 b instructs the remote station to raise itstransmission power, the remote station will do so without regard aswhether its transmissions are interfering with base station BS1 d or BS1e, as can occur when Nr is contained within Wr. This is the case becausethe remote station is only receiving power control information from BS3b. However, had the remote station been in soft handoff with all threebase stations, it would only raise its transmission power if all threebase stations had requested it to do so, thus reducing the chance thatthe remote station would raise its power level excessively.

Although the above embodiment describes how to facilitate a handoff froma single carrier base station to a multi-carrier base station, oneskilled in the art will appreciate that a similar method can be used tohandoff from a multi-carrier base station to a single carrier basestation. A handoff from a multi-carrier base station to a single carrierbase station could be used when a remote station is exitingmulti-carrier coverage, such as at point 540 or point 548.

In FIG. 8, in a second embodiment of the present invention, amulti-carrier handoff candidate is sent a soft handoff message thatinstructs the remote station to continue receiving single carriersignals from the single carrier base stations BS1, but also toadditionally begin receiving single carrier communications on frequencyNf from at least one multi-carrier base station BS3. In this embodiment,the infrastructure instructs these multi-carrier base stations B3 tobegin communications with the remote station using the single carrierprotocol both on the forward and reverse links in frequency bands Nf andNr, respectively. For instance, if the soft handoff were to occur atpoint 520, BS3 b would be instructed to begin single carriercommunications with the multi-carrier handoff candidate in frequencybands Nf and Nr.

While a remote station is in such a soft handoff, it has communicationlinks both with single carrier base stations BS1 and with multi-carrierbase stations BS3, and thus receives the communication path diversityand power control benefits provided by such a soft handoff. Namely, theremote station is receiving data from and transmitting data to multiplebase stations along different paths. Additionally, the remote station isreceiving power control feedback (commonly received in the form of powercontrol bits) from both the single carrier and multi-carrier basestations whose coverage area it is in, and thus is less likely to raiseits power transmission level to a point at which it unnecessarilyinterferes with one of these base stations. A diagram of thecommunication path after a handoff of this embodiment appears in FIG. 8,wherein the remote station continues transmitting in frequency band Nr,and wherein the remote station continues receiving single carriertransmissions in frequency band Nf from single carrier base stationsBS1. FIG. 8 also illustrates that the remote station begins receivingsingle carrier transmissions in frequency Nf from a multi-carrier basestation BS3. Additionally, remote station transmissions adhering to thesingle carrier protocol are received by single carrier base stations BS1and multi-carrier base station BS3.

Although the above describes a handoff from single carrier coverage tomixed coverage (an area that is both in the coverage of a single carrierbase station and in the coverage of a multi-carrier base station), whichoccurs, for instance, at point 520, one skilled in the art willappreciate that a similar method can be used to handoff frommulti-carrier coverage to mixed coverage, such as at point 540 or point548.

In the second handoff embodiment, once the remote station travels to apoint at which it is no longer in the coverage of single carrierbasestations BS1, such as point 530, the remote station will only becommunicating with multi-carrier base stations BS3, but will becommunicating with them using the single carrier protocol. At such apoint, a subsequent handoff can occur that will switch the mode ofcommunications from single carrier to multi-carrier. This subsequenthandoff comprises the infrastructure sending a handoff message to theremote station instructing it to stop single carrier communications witha set of at least one multi-carrier base station BS3 and to beginmulti-carrier communications on the same set of base stations infrequency bands Wf and Wr. In other words, the remote station is sent ahandoff message instructing it to cease all single carriercommunications, and to only communicate using the multi-carrier protocolon the forward and reverse links. In such an embodiment, theinfrastructure instructs the set of multi-carrier base stations BS3 toswitch its mode of communications with the remote station to themulti-carrier protocol in frequency bands Wf and Wr.

For instance, at point 530, a remote station which had performed ahandoff of the second handoff embodiment, and which was communicatingwith BS3 c in frequency bands Nf and Nr, using a single carrierprotocol, would be instructed to switch its mode of communication withBS3 c to a multi-carrier protocol in frequency bands Wf and Wr. Afterthis subsequent handoff, a diagram of the communication path looks onceagain as it did in FIG. 7.

Performing such a subsequent handoff is beneficial because it allows thebenefits of multi-carrier transmissions to be achieved. Whereinperforming multi-carrier transmissions on both the forward and reverselinks at a time when a remote station was in the coverage area of bothmulti-carrier and single carrier base stations, as was done in the firsthandoff embodiment, could have deleterious effects, performing thesetransmissions when not in a single carrier coverage area will not havethese deleterious effects, and thus should be performed after a remotestation exits the single carrier base stations' BS1 coverage areas.

A subsequent handoff that tells the remote station to only communicatewith one type of base station in that base station's native protocol(the native protocol of a multi-carrier base station is a multi-carrierprotocol, while the native protocol of a single carrier base station isa single carrier protocol) is not limited to a remote station travelingfrom a mixed coverage area to a multi-carrier coverage area, such as atpoint 530. Rather, a subsequent handoff message that instructs a remotestation to only communicate with single carrier base station's in asingle carrier protocol should be used when a remote station travelsfrom a mixed coverage area to a single carrier coverage area, such as atpoint 550.

The advantage of the second handoff embodiment of the present inventionover the first is that the use of soft handoff when in the coverage areaof both single carrier and multi-carrier base stations provides thebenefits of path diversity and decreases the chance of the remotestation interfering with one of the cells due to the fact that theremote station is receiving power control feedback from both types(single carrier and multi-carrier) of base stations. Although thissecond handoff embodiment provides these improvements over the first,there are considerations that still need to be taken into account inregards to the second handoff embodiment.

One such consideration is how the power levels of the multi-carrier basestations could be affected. Such consideration needs to be taken intoaccount because the transmission power needed to generate the spectraldensity used within a certain frequency bandwidth X to transmit Ninformation bits via a single carrier protocol is generally much greaterthan the transmission power needed to generate the spectral density usedin the same bandwidth X to transmit N information bits via amulti-carrier protocol. This consideration is best considered afterviewing FIGS. 9( a & b) and FIGS. 10( a & b).

FIG. 9 contains an illustration of the spectral density and theassociated transmission power that would be utilized to transmit Ninformation bits using an exemplary single carrier protocol of 1X (FIG.9 a), and it contains an illustration of the spectral density and theassociated transmission power that would be used to transmit the same Ninformation bits using an exemplary multi-carrier protocol of 3X (FIG. 9b).

The single carrier protocol modulates the information bits according toa single carrier modulation scheme and transmits the modulated bits at atransmission power Pn, in a frequency band having a bandwidth of Bn.Hereinafter, a given spectral density will be addressed usingcross-product notation. For example, in FIG. 9 a, Pn is the power usedto generate the signal over a bandwidth Bn; thus, the spectral densityof the diagrammed single carrier signal in FIG. 9 a would be referred toas Pn×Bn.

The multi-carrier protocol modulates the information bits according to amulti-carrier modulation scheme and transmits the modulated bits at atransmission power of Pw at each frequency band Bn in frequency band Bw.The multi-carrier signal has a full spectral density of Pw×Bw.

The power Pn is greater than Pw, while the bandwidth Bw is greater thanthe bandwidth Bn. Using 3X as the exemplary multi-carrier protocol and1X as the exemplary single carrier protocol, the bandwidth Bw iscomprised of three Bn-sized chunks. As is seen, the spectral density ina particular bandwidth Bn is much greater for a 1X single carrier signalthan it is for a 3X multi-carrier signal. Likewise, the transmissionpower, Pn, used to generate the spectral density Pn×Bn is approximatelythree times the power level, Pw, used to generate the spectral densityPw×Bn in each Bn frequency chunk.

FIG. 10 a and FIG. 10 b show two alternate embodiments in which amulti-carrier base station BS3 could simultaneously transmit a singlecarrier signal to a first remote station and a multi-carrier signal to asecond remote station.

In FIG. 10 a, the embodiment entitled “Dual Transmission UtilizingOverlapping Frequencies,” assumes that in the non-homogenous network 410the single carrier frequency band Nf is contained within themulti-carrier frequency band Wf. Such a non-homogenous network willhereinafter be referred to as an overlapping non-homogenous network.Diagrammed in FIG. 10 a is the transmission power and spectral densityutilized in various frequency bands to transmit to two remote stations,the first of which is in a soft-handoff of the second handoffembodiment, wherein the single carrier protocol is a 1X protocol, thesecond of which is communicating with BS3 in accordance to a 3Xmulti-carrier protocol. In an overlapping non-homogenous network,multi-carrier base station BS3 transmits in frequency band 1010, whichis comprised of frequency bands 1020, 1030, and 1040, a signal modulatedin accordance with a multi-carrier protocol that is intended for thesecond remote station. Additionally, multi-carrier base station BS3transmits in frequency band 1020 a signal, modulated in accordance witha single carrier protocol, intended for the first remote station.Assuming that a different power amplifier is used for each band 1020,1030, and 1040, the transmission power used by each amplifiers of BS3 togenerate the spectral density of the multi-carrier signal in frequencybands 1030 and 1040 is Pw. The transmission power used by the amplifierof BS3 to generate the spectral density of the single carrier andmulti-carrier signal in frequency band 1020 is a Pn+Pw, a sum of thetransmission power needed to transmit the single carrier modulatedsignal and the transmission power needed to transmit the multi-carriermodulated signal. Frequency band 1010 is representative of Wf, andfrequency band 1020 is representative of Nf.

In FIG. 10 b, the embodiment entitled “Dual Transmission UtilizingNon-overlapping Frequencies,” assumes that in the non-homogenous network410 the single carrier frequency band Nf is located outside themulti-carrier frequency band Wf. Such a non-homogenous network willhereinafter be referred to as a non-overlapping non-homogenous network.Diagrammed in FIG. 10 b is the transmission power utilized in variousfrequency bands to transmit to two remote stations, the first of whichis in a soft-handoff of the second handoff embodiment, wherein thesingle carrier protocol is a 1X protocol, the second of which iscommunicating with BS3 in accordance to a 3X multi-carrier protocol. Ina non-overlapping non-homogenous network, multi-carrier base station BS3transmits in frequency band 1050, which comprises frequency bands 1060,1070, and 1080, a signal modulated in accordance with a multi-carrierprotocol that is intended for the second remote station. Additionally,multi-carrier base station BS3 transmits in frequency band 1090, asignal modulated in accordance with a single carrier protocol intendedfor the first remote station. Assuming that a different power amplifieris used for each band 1060, 1070, and 1080, the transmission power usedby each amplifier of BS3 to generate the spectral density of themulti-carrier signal in frequency bands 1060, 1070, and 1080, is Pw. Thetransmission power used by an amplifier of BS3 to generate the spectraldensity of the single carrier signal in frequency band 1090 is Pn. Inthis case, frequency band 1050 is representative of Wf, and frequencyband 1090 is representative of Nf. As described above, the secondhandoff embodiment of the present invention could affect power levels.Telecommunications systems, such as cdma2000 systems, are generallypower limited in the sense that each amplifier can only transmit acertain amount of power. In an overlapping non-homogenous network, thishas ramifications as follows. As an example, consider a multi-carrierbase station BS3, in a non-homogenous network, each BS3 amplifier havinga maximum transmission power limit of 5*Pw. This means that BS3 couldsupport communications with up to five remote stations simultaneously.However, this number decreases when BS3 communicates in single carriermode with remote stations that are in soft handoff. FIG. 11 and FIG. 12serve to visualize this.

In FIG. 11, the transmission power of one multi-carrier call isillustrated, wherein 5*Pw is the maximum allowable transmission powerlevel for a given multi-carrier base station BS3. It should be clear toone skilled in the art that given this maximum power level,multi-carrier base station BS3 could still support four more calls inaddition to the one call currently up, because each multi-carrier callutilizes an average transmission power level of Pw per amplifier.However, bringing up a single carrier call on this same base stationdrastically reduces this capacity, as illustrated in FIG. 12.

In FIG. 12, the transmission power of one multi-carrier call inconjunction with a single carrier call on a multi-carrier base stationBS3 is illustrated. It should be clear to one skilled in the art thatonly one more multi-carrier call can be added at this point, and that nomore soft handoff calls can be added to at this point due to the nearsaturation power level of the amplifier supporting frequency band Nf.

Although the example of a power limit of 5*Pw is smaller than one couldexpect in a real system, it serves to clearly illustrate that theavailable multi-carrier call capacity of a multi-carrier base stationcan decrease as the base station begins to transmit data on the forwardlink in compliance with a single carrier protocol. Thus, in anoverlapping non-homogenous network, the second handoff embodiment canhave a deleterious effect on multi-carrier call capacity. Thisdeleterious effect does not occur in a non-overlapping non-homogenousnetwork, as multi-carrier base station BS3 would use two distinctlyseparate frequencies for multi-carrier calls and single carrier calls,wherein each frequency is supported by its own amplifier, as illustratedin FIG. 10 b. However, it might be more costly to purchase the rights tothe extra frequency spectrum needed to create a non-overlappingnon-homogenous network, and the deployment costs for the extratransmitters might prove costly as well.

Also, looking at the spectral density distribution in FIG. 12, oneskilled in the art will understand that for each remote station in ahandoff of the second handoff embodiment, interference in the singlecarrier frequency band Nf (1020 in FIG. 10 a) is higher than it would beif either the base station BS3 transmitted data to the multi-carrierhandoff candidate in accordance with a single carrier protocol in afrequency band other than Nf, or if base station BS3 transmitted data tothe multi-carrier handoff candidate in accordance with a multi-carrierprotocol (thus distributing the spectral density of the transmissionacross a wider frequency band).

Another thing to consider in relation to the second handoff embodimentof the present invention is that, while the remote station is insoft-handoff, the fact that it is only engaging in single carriercommunications will limit the forward link data transmission rate. Thisis a very important consideration. In many communication systems, themulti-carrier protocols provide a means for a remote station to receivemuch more data on the forward link than do single carrier protocols.Thus, one advantage that the first handoff embodiment has over thesecond handoff embodiment is that higher data rate transmission canbegin occurring while the remote station is within multi-carriercoverage in the first handoff embodiment, whereas in the second handoffembodiment, a remote station would not begin receiving higher data ratetransmissions until it is out of single carrier coverage.

Other embodiments of the present invention combine the advantages of thefirst handoff embodiment with those of the second handoff embodiment. Inthe below handoff embodiments, a multi-carrier handoff candidate is senta handoff message that instructs the remote station to switch its modeof reception to a multi-carrier mode, but to transmit in a singlecarrier mode. In other words, the multi-carrier handoff candidate issent a message that has it switch from a mode wherein it behaves likeremote station 220 a of FIG. 2 to a mode wherein it behaves like remotestation 110 a of FIG. 1. Several of these embodiments are describedbelow.

In FIG. 13, in a third handoff embodiment of the present invention, amulti-carrier handoff candidate is sent a handoff message that instructsthe remote station to continue transmitting data in accordance with asingle carrier protocol in Nr, and to begin receiving data in accordancewith a multi-carrier protocol in Wf from at least one multi-carrier basestation BS3. In this embodiment, the remote station uses the samefrequency band Nr for the transmission of data after the handoff as itused for the transmission of data before the handoff. The infrastructureinstructs these multi-carrier base stations BS3 to begin transmittingdata to the remote station on the forward link using the multi-carrierprotocol in frequency band Wf. Additionally, the infrastructureinstructs these multi-carrier base stations BS3 to begin receivingreverse link transmissions from the remote station in accordance withthe single carrier protocol in frequency band Nr. For instance, if thehandoff were to occur at point 520, multi-carrier base station BS3 bwould be instructed to begin transmitting data to the remote station infrequency band Wf in accordance with the multi-carrier protocol.Additionally, single carrier base stations BS1 d and BS1 e would beinstructed to stop transmitting data to the remote station, but would beinstructed, either actively (by instruction) or passively (by lack ofinstruction), to continue receiving single carrier communications infrequency band Nr from the remote station. The remote station would beinstructed, via a handoff message, to continue transmitting data as itwas before, in accordance with the single carrier protocol in frequencyband Nr, but to begin receiving data in accordance with themulti-carrier protocol on frequency Wf from base station BS3 b. Adiagram of an exemplary communication path after the handoff of thethird embodiment appears in FIG. 13, wherein the remote stationcontinues transmitting in frequency band Nr, and begins receiving infrequency band Wf, and wherein transmissions adhering to the singlecarrier protocol are received by two single carrier base stations BS1and one multi-carrier base station BS3, and wherein base station BS3begins transmitting in accordance with the multi-carrier protocol infrequency band Wf.

Although the above describes a handoff from single carrier coverage tomixed coverage (an area that is both in the coverage of a single carrierbase station and in the coverage of a multi-carrier base station), whichoccurs, for instance, at point 520, one skilled in the art willappreciate that a similar method can be used to handoff frommulti-carrier coverage to mixed coverage, such as at point 540 or point548.

In the third handoff embodiment, once the remote station travels to apoint at which it is no longer in the coverage of single carrierbasestations BS1, such as point 530, a subsequent handoff can occur thatwill switch the mode of communications from single carrier tomulti-carrier. This subsequent handoff comprises the infrastructuresending a handoff message to the remote station instructing it to stopsingle carrier communications with a set of at least one multi-carrierbase station BS3 and to begin multi-carrier communications on the sameset of base stations in frequency bands Wf and Wr. In other words, theremote station is sent a handoff message instructing it to cease allsingle carrier communications, and to only communicate using themulti-carrier protocol on the forward and reverse links. In such anembodiment, the infrastructure instructs the set of multi-carrier basestations BS3 to switch their modes of communications with the remotestation to the multi-carrier protocol in frequency bands Wf and Wr.

A subsequent handoff that tells the remote station to only communicatewith one type of base station in that base station's native protocol isnot limited to a remote station traveling from a mixed coverage area toa multi-carrier coverage area, such as at point 530. Rather, asubsequent handoff message that instructs a remote station to onlycommunicate with single carrier base station's in a single carrierprotocol should be used when a remote station travels from a mixedcoverage area to a single carrier coverage area, such as at point 550.

This third handoff embodiment offers improvements over the secondhandoff embodiment in relation to the considerations that were discussedearlier. In the third handoff embodiment, the transmission power used bythe multi-carrier base stations to transmit to the remote station is notdisproportionately increased on one channel. For instance, FIG. 12illustrated that during soft handoff of a method of the second handoffembodiment, a multi-carrier base station BS3 would be limited (due totransmit power limitations) to supporting one more multi-carrier call,and would not be able to support any more soft handoffs. However, givena similar situation, in which a single multi-carrier call and a singlesoft handoff are in progress, but wherein the single soft handoff isperformed according to the method of the third handoff embodiment, amulti-carrier base station's transmit power limitations do not causesuch severe limitations. This is because, in the method of the thirdhandoff embodiment, the remote station in handoff is sent multi-carriersignals rather than single carrier signals. Power transmission on amulti-carrier base station that was servicing one remote station priorto engaging in a soft handoff with another remote station, asillustrated in FIG. 11, would therefore transition to a powertransmission state like that shown in FIG. 14 after initiating a softhandoff with another remote station per the method of the third handoffembodiment. As shown in FIG. 14, the transmission power for the remotestation in handoff is evenly spread across the three sub-bands offrequency band Wf. Thus, in this example, wherein max transmission powerlevel is 5*Pw, and wherein a soft-handoff per the method of the thirdhandoff embodiment is in with one remote station while anothermulti-carrier call is in progress with another remote station, it isseen that the multi-carrier base station is able to transmit to threemore remote stations, each of which can either be in a puremulti-carrier mode or in a soft-handoff mode. This is a vast improvementover the power limitations that occur due to the soft handoff of thesecond handoff embodiment, as described in relation to FIG. 12.

Another way in which the third handoff embodiment has advantages overthe method of the second handoff embodiment is that higher data ratetransmission can begin occurring on the forward link as soon as theremote station enters multi-carrier coverage.

Although the third handoff embodiment does offer some advantages, someconsiderations should be taken into account with the third handoffembodiment. For instance, although the third handoff embodiment providespath diversity on the reverse link, it does not provide the pathdiversity on the forward link that is provided for by the method of thesecond handoff embodiment. Additionally, the third handoff embodimentonly provides power control feedback from the multi-carrier base stationwhile in soft handoff. As discussed in reference to the first handoffembodiment, a remote station that is only receiving power controlfeedback from the multi-carrier base stations could inadvertentlytransmit at an excessively high power, and thus interfere with thesingle carrier base stations whose coverage the remote station is in. Asolution to this problem of power control can be provided in thishandoff embodiment, as well as in any others that have theaforementioned power control problem.

Such a solution is as follows. One or more of the single carrier basestations BS1 that is receiving transmissions from the remote stationgenerates a message containing power control information related to theremote station in question. The information can be as simple as whetherthe remote station should lower its power, or it can contain moredetailed information on the signal being received from the remotestation in question. The single carrier base stations send thesemessages via the infrastructure backhaul to one or more multi-carrierbase stations that are communicating with the remote station. Knowledgeof the backhaul and how to send messages over it would be known by oneskilled in the art. The multi-carrier base station uses this receivedinformation when determining whether it should send a power control bitto the remote station that indicates an increase or a decrease intransmission power. Due to delays and bandwidth constraints on thebackhaul, however, this solution will likely prove impractical. In sucha case, the problem of possible interference in the single carriersystem due to excessive transmission power by the remote station wouldremain in the third handoff embodiment.

In FIG. 15, a fourth handoff embodiment addresses the problem ofinterference on the reverse link in a different manner. In the fourthhandoff embodiment, a soft handoff similar to that found in the thirdhandoff embodiment is used, wherein multi-carrier communications areused by the multi-carrier base stations to transmit data to the remotestation on the forward link, and wherein single carrier communicationsare used by the remote station to transmit data to the base stations onthe reverse link. The difference between the third handoff embodimentand the fourth handoff embodiment is as follows. In the soft handoff ofthe third handoff embodiment, the remote station transmits data in thesingle carrier frequency band Nr both before and after the handoff. Incontrast, in the fourth handoff embodiment the remote station transmitsdata after handoff in a single carrier frequency band that is differentfrom the single carrier frequency band used prior to handoff. Thisdifference is illustrated by transforming the labeling of the reverselink in FIG. 13 from Nr to a label of Nra, as shown in FIG. 15. WhereasNr is representative of the reverse link frequency band used by thesingle carrier systems for remote stations that are not in soft-handoffwith multi-carrier base stations (and it is also representative of thereverse link frequency band used by remote stations involved in ahandoff of the second and third embodiments), Nra is representative of asingle carrier frequency band reverse link that is located outside ofthe frequency band Nr. By having the remote station utilize a differentsingle carrier frequency band for the reverse link while in softhandoff, it removes the problem of possible interference in the singlecarrier system due to the use of excessive transmission power by theremote station. The alternative single carrier reverse link frequencyband, denoted by Nra in FIG. 15, is contained within the frequency bandWr in an exemplary embodiment. In an alternative embodiment, Nra iscontained outside the frequency band Wr.

Although the above describes a handoff from single carrier coverage tomixed coverage (an area that is both in the coverage of a single carrierbase station and in the coverage of a multi-carrier base station), whichoccurs, for instance, at point 520, one skilled in the art willappreciate that a similar method can be used to handoff frommulti-carrier coverage to mixed coverage, such as at point 540 or point548.

In the fourth handoff embodiment, once the remote station travels to apoint at which it is no longer in the coverage of single carrierbasestations BS1, such as point 530, a subsequent handoff can occur thatwill switch the mode of communications from single carrier tomulti-carrier. This subsequent handoff comprises the infrastructuresending a handoff message to the remote station instructing it to stopsingle carrier communications with a set of at least one multi-carrierbase station BS3 and to begin multi-carrier communications on the sameset of base stations in frequency bands Wf and Wr. In other words, theremote station is sent a handoff message instructing it to cease allsingle carrier communications, and to only communicate using themulti-carrier protocol on the forward and reverse links. In such anembodiment, the infrastructure instructs the set of multi-carrier basestations BS3 to switch its mode of communications with the remotestation to the multi-carrier protocol in frequency bands Wf and Wr.

A subsequent handoff that tells the remote station to only communicatewith one type of base station in that base station's native protocol isnot limited to a remote station traveling from a mixed coverage area toa multi-carrier coverage area, such as at point 530. Rather, asubsequent handoff message that instructs a remote station to onlycommunicate with single carrier base station's in a single carrierprotocol should be used when a remote station travels from a mixedcoverage area to a single carrier coverage area, such as at point 550.

In the fourth handoff embodiment, the infrastructure instructs theremote station, via a handoff message, to begin transmitting data inaccordance with a single carrier protocol in frequency band Nra, and tobegin receiving data in accordance with a multi-carrier protocol infrequency band Wf from at least one multi-carrier base station BS3. Theinfrastructure instructs these multi-carrier base stations BS3 to begintransmitting data to the remote station on the forward link using themulti-carrier protocol in frequency band Wf. Additionally, theinfrastructure instructs these multi-carrier base stations BS3 to beginreceiving reverse link transmissions from the remote station inaccordance with the single carrier protocol in frequency band Nra. Also,the infrastructure instructs the single carrier base stations BS1involved in the handoff to switch its reception of reverse linktransmission from the remote station from frequency band Nr to frequencyband Nra (described in reference to the fourth handoff embodiment).

Although the above describes a handoff from single carrier coverage tomixed coverage (an area that is both in the coverage of a single carrierbase station and in the coverage of a multi-carrier base station), whichoccurs, for instance, at point 520, one skilled in the art willappreciate that a similar method can be used to handoff frommulti-carrier coverage to mixed coverage, such as at point 540 or point548.

In the fourth handoff embodiment, once the remote station travels to apoint at which it is no longer in the coverage of single carrierbasestations BS1, such as point 530, a subsequent handoff can occur thatwill switch the mode of communications from single carrier tomulti-carrier. This subsequent handoff comprises the infrastructuresending a handoff message to the remote station instructing it to stopsingle carrier communications with a set of at least one multi-carrierbase station BS3 and to begin multi-carrier communications on the sameset of base stations in frequency bands Wf and Wr. In other words, theremote station is sent a handoff message instructing it to cease allsingle carrier communications, and to only communicate using themulti-carrier protocol on the forward and reverse links. In such anembodiment, the infrastructure instructs the set of multi-carrier basestations BS3 to switch its mode of communications with the remotestation to the multi-carrier protocol in frequency bands Wf and Wr.

A subsequent handoff that tells the remote station to only communicatewith one type of base station in that base station's native protocol isnot limited to a remote station traveling from a mixed coverage area toa multi-carrier coverage area, such as at point 530. Rather, asubsequent handoff message that instructs a remote station to onlycommunicate with single carrier base station's in a single carrierprotocol should be used when a remote station travels from a mixedcoverage area to a single carrier coverage area, such as at point 550.

FIG. 16 illustrates a remote station in a handoff of a fifth handoffembodiment, which differs from the fourth handoff embodiment only inthat the single carrier base stations do not receive the reverse linktransmissions from the remote station that is in a soft-handoff.Although it is desirable that the single carrier base stations receivethe single carrier transmissions from the remote station for pathdiversification, it may be cost prohibitive to configure the singlecarrier base stations BS1 to receive single carrier signals in twofrequency bands, one for remote stations not in soft handoff, and onefor remote stations in soft handoff. The fifth handoff embodiment can beused in cases wherein it is not desired to perform the configurationsneeded to receive transmissions in two frequency bands on single carrierbase stations BS1. In the fifth handoff embodiment, the multi-carrierbase stations BS3 and the remote station perform the same way as in thefourth handoff embodiment. The only difference, in fact, between thefourth and the fifth handoff embodiment are that the single carrier basestations BS1 is not used for communications with the remote stationafter a handoff of the fifth handoff embodiment.

In the fifth handoff embodiment, the infrastructure instructs the remotestation, via a handoff message, to stop communicating with the singlecarrier base stations BS1 and to begin transmitting data in accordancewith a single carrier protocol in frequency band Nra, and to beginreceiving data in accordance with a multi-carrier protocol in frequencyband Wf from at least one multi-carrier base station BS3. In such anembodiment, the infrastructure instructs these multi-carrier basestations BS3 to begin transmitting data to the remote station on theforward link using the multi-carrier protocol in frequency band Wf.Additionally, the infrastructure instructs these multi-carrier basestations BS3 to begin receiving reverse link transmissions from theremote station in accordance with the single carrier protocol infrequency band Nra. Also, the infrastructure instructs the singlecarrier base stations BS1 to stop communications with the remotestation.

The disadvantage of the fifth handoff embodiment over the fourth handoffembodiment is that reverse link path diversity that was provided by thefourth handoff embodiment is not present in the fifth handoffembodiment.

Although the above describes a handoff from single carrier coverage tomixed coverage (an area that is both in the coverage of a single carrierbase station and in the coverage of a multi-carrier base station), whichoccurs, for instance, at point 520, one skilled in the art willappreciate that a similar method can be used to handoff frommulti-carrier coverage to mixed coverage, such as at point 540 or point548.

In the fifth handoff embodiment, once the remote station travels to apoint at which it is no longer in the coverage of single carrierbasestations BS1, such as point 530, a subsequent handoff can occur thatwill switch the mode of communications from single carrier tomulti-carrier. This subsequent handoff comprises the infrastructuresending a handoff message to the remote station instructing it to stopsingle carrier communications with a set of at least one multi-carrierbase station BS3 and to begin multi-carrier communications on the sameset of base stations in frequency bands Wf and Wr. In other words, theremote station is sent a handoff message instructing it to cease allsingle carrier communications, and to only communicate using themulti-carrier protocol on the forward and reverse links. In such anembodiment, the infrastructure instructs the set of multi-carrier basestations BS3 to switch its mode of communications with the remotestation to the multi-carrier protocol in frequency bands Wf and Wr.

A subsequent handoff that tells the remote station to only communicatewith one type of base station in that base station's native protocol isnot limited to a remote station traveling from a mixed coverage area toa multi-carrier coverage area, such as at point 530. Rather, asubsequent handoff message that instructs a remote station to onlycommunicate with single carrier base station's in a single carrierprotocol should be used when a remote station travels from a mixedcoverage area to a single carrier coverage area, such as at point 550.

One thing that is not provided for in any of the aforementioned handoffembodiments in which the forward link transmissions adhere to themulti-carrier protocol (namely, the third-fifth embodiments) is forwardlink path diversity from both the single carrier and the multi-carrierbase stations. However, in the handoff embodiments described below,forward link path diversity from both the single carrier and themulti-carrier base stations is achieved, at least in part. This is doneby configuring the single carrier base stations BS1 to transmit signalsto the remote station in the single carrier frequency band Nf, whereinthe transmitted signal is a portion of a signal that was generated inaccordance with the multi-carrier protocol. The concept of transmittingin a single carrier frequency band a portion of a signal that wasgenerated in accordance with a multi-carrier protocol is describedbelow.

A multi-carrier frequency band can be logically partitioned into severalsections, each having a frequency bandwidth of a single carrierfrequency band. In an exemplary system wherein Nf is contained withinWf, and wherein single carrier transmissions are performed using the 1Xprotocol and multi-carrier transmissions are performed using the 3Xprotocol, the multi-carrier frequency band Wf can be partitioned intothree sub-bands, which will be called Wf_(a), Wf_(b), and Wf_(c),wherein each sub-band has a width equal to that of Nf. In an exemplarycase, Nf is the same frequency band as Wf_(c). However, it will beunderstood by one skilled in the art that Nf can be present anywherewithin Wf.

FIG. 17 a illustrates this exemplary case, in which Wf is divided intothree sub-bands, each of equal width, wherein the third sub-band,Wf_(c), is the same frequency band as the single carrier frequency bandNf. FIG. 17 a also shows an exemplary multi-carrier signal, S, thatwould be transmitted in Wf. The signal S can likewise be broken up intothree sub-signals, S_(a), S_(b), and S_(c), each of which is transmittedover their respective sub-band. In this case S_(c) is transmitted overfrequency band Nf (also known as Wf_(c)). In the below described handoffembodiments, the entire multi-carrier signal, signal S, will betransmitted in frequency band Wf by the multi-carrier base stations.S_(c) is a portion of the signal, S, generated in accordance with themulti-carrier protocol, that is transmitted in the frequency band Nf. Togain path diversity for this portion of the signal, in the belowdescribed handoff embodiments, the single carrier base stations BS1 thatare transmitting signals in frequency band Nf in accordance with thesingle carrier protocol additionally transmit the portion of themulti-carrier signal that was transmitted in the frequency band Nf bythe multi-carrier base stations. For instance, if a signal weregenerated and transmitted as per FIG. 17 a, then in the handoffembodiments described below the portion S_(c) would be transmitted bysingle carrier base stations, as illustrated in FIG. 17 b.

FIG. 18 illustrates a remote station in a handoff of a sixth handoffembodiment. The sixth handoff embodiment has all of the communicationpaths of the third handoff embodiment, plus it also has a single carrierforward link communication path between the single carrier base stationsBS1 and the remote station. As illustrated, portion S_(c) of themulti-carrier signal is transmitted over these single carrier forwardlink communication paths. Portion S_(c) is also transmitted as part ofthe multi-carrier signal transmitted by multi-carrier base station BS3.The sixth handoff embodiment has all of the advantages of the thirdhandoff embodiment, and additionally it has the advantage that it gainsadditional forward link path diversity from the single carrier basestations for the portion of the multi-carrier signal that is transmittedby both the multi-carrier and single carrier base stations.

In the sixth handoff embodiment of the present invention, amulti-carrier handoff candidate is sent a handoff message that instructsthe remote station to continue transmitting data in accordance with asingle carrier protocol in Nr, and to begin receiving data in accordancewith a multi-carrier protocol in Wf from at least one multi-carrier basestation BS3. The handoff message also instructs the remote station tobegin receiving data in accordance with a multi-carrier protocol in Nffrom at least one single carrier base station BS1. In one embodiment theremote station is instructed to only decode the portion of the signalthat occurs in the single carrier frequency band because the singlecarrier base stations BS1 will only be transmitting a portion of themulti-carrier signal.

In an alternative embodiment, the remote station is simply instructed todecode the entire multi-carrier signal from the single carrier basestations BS1. In such an embodiment, although the remote station willnot be able to decode the entire expected multi-carrier signal from BS1,but rather only the portion that was transmitted by BS1, the absence ofsome of the signal will not negatively impact the remote station whendecoding the entire multi-carrier signal as received from BS3.

In the sixth handoff embodiment, the remote station uses the samefrequency band Nr for the transmission of data after the handoff as itused for the transmission of data before the handoff. In such anembodiment, the infrastructure instructs these multi-carrier basestations BS3 to begin transmitting data to the remote station on theforward link using the multi-carrier protocol in frequency band Wf.Additionally, the infrastructure instructs these multi-carrier basestations BS3 to begin receiving reverse link transmissions from theremote station in accordance with the single carrier protocol infrequency band Nr. Also, the infrastructure instructs these singlecarrier base stations BS1 to begin generating signals in accordance witha multi-carrier protocol and to transmit in frequency band Nf theportion of each of these signals that will be similarly transmitted infrequency band Nf by the multi-carrier base stations BS3. Single carrierbase stations BS1 are instructed, either actively (by instruction) orpassively (by lack of instruction), to continue receiving single carriercommunications in frequency band Nr from the remote station.

Although the above describes a handoff from single carrier coverage tomixed coverage (an area that is both in the coverage of a single carrierbase station and in the coverage of a multi-carrier base station), whichoccurs, for instance, at point 520, one skilled in the art willappreciate that a similar method can be used to handoff frommulti-carrier coverage to mixed coverage, such as at point 540 or point548.

In the sixth handoff embodiment, once the remote station travels to apoint at which it is no longer in the coverage of single carrierbasestations BS1, such as point 530, a subsequent handoff can occur thatwill switch the mode of communications from single carrier tomulti-carrier. This subsequent handoff comprises the infrastructuresending a handoff message to the remote station instructing it to stopsingle carrier communications with a set of at least one multi-carrierbase station BS3 and to begin multi-carrier communications on the sameset of base stations in frequency bands Wf and Wr. In other words, theremote station is sent a handoff message instructing it to cease allsingle carrier communications, and to only communicate using themulti-carrier protocol on the forward and reverse links. In such anembodiment, the infrastructure instructs the set of multi-carrier basestations BS3 to switch its mode of communications with the remotestation to the multi-carrier protocol in frequency bands Wf and Wr.

A subsequent handoff that tells the remote station to only communicatewith one type of base station in that base station's native protocol isnot limited to a remote station traveling from a mixed coverage area toa multi-carrier coverage area, such as at point 530. Rather, asubsequent handoff message that instructs a remote station to onlycommunicate with single carrier base station's in a single carrierprotocol should be used when a remote station travels from a mixedcoverage area to a single carrier coverage area, such as at point 550.

FIG. 19 illustrates a remote station in a handoff of a seventh handoffembodiment. The seventh handoff embodiment has all of the communicationpaths of the fourth handoff embodiment, plus it also has a singlecarrier forward link communication path between the single carrier basestations and the remote station. As illustrated, portion S_(c) of themulti-carrier signal is transmitted over these single carrier forwardlink communication paths. Portion S_(c) is also transmitted as part ofthe multi-carrier signal transmitted by multi-carrier base station BS3.The seventh handoff embodiment has all of the advantages of the fourthhandoff embodiment, and additionally it has the advantage that it gainsforward link path diversity for the portion of the multi-carrier signalthat is transmitted by both the multi-carrier and single carrier basestations.

In the seventh handoff embodiment, the infrastructure instructs theremote station, via a handoff message, to begin transmitting data inaccordance with a single carrier protocol in frequency band Nra(described in reference to the fourth handoff embodiment), and to beginreceiving data in accordance with a multi-carrier protocol in frequencyband Wf from at least one multi-carrier base station BS3. The handoffmessage also instructs the remote station to begin receiving data inaccordance with a multi-carrier protocol in Nf from at least one singlecarrier base station BS1. In one embodiment the remote station isinstructed to only decode the portion of the signal that occurs in thesingle carrier frequency band because the single carrier base stationsBS1 will only be transmitting a portion of the multi-carrier signal. Inan alternative embodiment, the remote station is simply instructed todecode the entire multi-carrier signal from the single carrier basestations BS1. In such an embodiment, although the remote station willnot be able to decode the entire expected multi-carrier signal from BS1,but rather only the portion that was transmitted by BS1, the absence ofsome of the signal will not negatively impact the remote station whendecoding the entire multi-carrier signal as received from BS3.

In the seventh embodiment, the infrastructure instructs thesemulti-carrier base stations BS3 to begin transmitting data to the remotestation on the forward link using the multi-carrier protocol infrequency band Wf. Additionally, the infrastructure instructs thesemulti-carrier base stations BS3 to begin receiving reverse linktransmissions from the remote station in accordance with the singlecarrier protocol in frequency band Nra. Also, the infrastructureinstructs these single carrier base stations BS1 to begin generatingsignals in accordance with a multi-carrier protocol and to transmit infrequency band Nf the portion of each of these signals that will besimilarly transmitted in frequency band Nf by the multi-carrier basestations BS3. As well, the infrastructure instructs these single carrierbase stations BS1 involved in the handoff to switch its reception ofreverse link transmission from the remote station from frequency band Nrto frequency band Nra.

Although the above describes a handoff from single carrier coverage tomixed coverage (an area that is both in the coverage of a single carrierbase station and in the coverage of a multi-carrier base station), whichoccurs, for instance, at point 520, one skilled in the art willappreciate that a similar method can be used to handoff frommulti-carrier coverage to mixed coverage, such as at point 540 or point548.

In the seventh handoff embodiment, once the remote station travels to apoint at which it is no longer in the coverage of single carrierbasestations BS1, such as point 530, a subsequent handoff can occur thatwill switch the mode of communications from single carrier tomulti-carrier. This subsequent handoff comprises the infrastructuresending a handoff message to the remote station instructing it to stopsingle carrier communications with a set of at least one multi-carrierbase station BS3 and to begin multi-carrier communications on the sameset of base stations in frequency bands Wf and Wr. In other words, theremote station is sent a handoff message instructing it to cease allsingle carrier communications, and to only communicate using themulti-carrier protocol on the forward and reverse links. In such anembodiment, the infrastructure instructs the set of multi-carrier basestations BS3 to switch its mode of communications with the remotestation to the multi-carrier protocol in frequency bands Wf and Wr.

A subsequent handoff that tells the remote station to only communicatewith one type of base station in that base station's native protocol isnot limited to a remote station traveling from a mixed coverage area toa multi-carrier coverage area, such as at point 530. Rather, asubsequent handoff message that instructs a remote station to onlycommunicate with single carrier base station's in a single carrierprotocol should be used when a remote station travels from a mixedcoverage area to a single carrier coverage area, such as at point 550.

FIG. 20 illustrates a remote station in a handoff of an eighth handoffembodiment. The eighth handoff embodiment has all of the communicationpaths of the fifth handoff embodiment, plus it also has a single carrierforward link communication path between the single carrier base stationsand the remote station. As illustrated, portion S_(c) of themulti-carrier signal is transmitted over these single carrier forwardlink communication paths. Portion S_(c) is also transmitted as part ofthe multi-carrier signal transmitted by multi-carrier base station BS3.The eighth handoff embodiment has all of the advantages of the fifthhandoff embodiment, and additionally it has the advantage that it gainsforward link path diversity for the portion of the multi-carrier signalthat is transmitted by both the multi-carrier and single carrier basestations.

In this embodiment, the infrastructure instructs the remote station, viaa handoff message, to begin transmitting data in accordance with asingle carrier protocol in frequency band Nra (described in reference tothe fourth handoff embodiment), and to begin receiving data inaccordance with a multi-carrier protocol in frequency band Wf from atleast one multi-carrier base station BS3. The handoff message alsoinstructs the remote station to begin receiving data in accordance witha multi-carrier protocol in Nf from at least one single carrier basestation BS1. In one embodiment the remote station is instructed to onlydecode the portion of the signal that occurs in the single carrierfrequency band because the single carrier base stations BS1 will only betransmitting a portion of the multi-carrier signal. In an alternativeembodiment, the remote station is simply instructed to decode the entiremulti-carrier signal from the single carrier base stations BS1. In suchan embodiment, although the remote station will not be able to decodethe entire expected multi-carrier signal from BS1, but rather only theportion that was transmitted by BS1, the absence of some of the signalwill not negatively impact the remote station when decoding the entiremulti-carrier signal as received from BS3.

In such an embodiment, the infrastructure instructs these multi-carrierbase stations BS3 to begin transmitting data to the remote station onthe forward link using the multi-carrier protocol in frequency band Wf.Additionally, the infrastructure instructs these multi-carrier basestations BS3 to begin receiving reverse link transmissions from theremote station in accordance with the single carrier protocol infrequency band Nra. Also, the infrastructure instructs these singlecarrier base stations BS1 to begin generating signals in accordance witha multi-carrier protocol and to transmit in frequency band Nf theportion of each of these signals that will be similarly transmitted infrequency band Nf by the multi-carrier base stations BS3. Single carrierbase stations BS1 are instructed to stop receiving single carriercommunications from the remote station.

Although the above describes a handoff from single carrier coverage tomixed coverage (an area that is both in the coverage of a single carrierbase station and in the coverage of a multi-carrier base station), whichoccurs, for instance, at point 520, one skilled in the art willappreciate that a similar method can be used to handoff frommulti-carrier coverage to mixed coverage, such as at point 540 or point548. Example 3, below, speaks to this.

In the eighth handoff embodiment, once the remote station travels to apoint at which it is no longer in the coverage of single carrierbasestations BS1, such as point 530, a subsequent handoff can occur thatwill switch the mode of communications from single carrier tomulti-carrier. This subsequent handoff comprises the infrastructuresending a handoff message to the remote station instructing it to stopsingle carrier communications with a set of at least one multi-carrierbase station BS3 and to begin multi-carrier communications on the sameset of base stations in frequency bands Wf and Wr. In other words, theremote station is sent a handoff message instructing it to cease allsingle carrier communications, and to only communicate using themulti-carrier protocol on the forward and reverse links. In such anembodiment, the infrastructure instructs the set of multi-carrier basestations BS3 to switch its mode of communications with the remotestation to the multi-carrier protocol in frequency bands Wf and Wr.Example 2, below, speaks to this.

A subsequent handoff that tells the remote station to only communicatewith one type of base station in that base station's native protocol isnot limited to a remote station traveling from a mixed coverage area toa multi-carrier coverage area, such as at point 530. Rather, asubsequent handoff message that instructs a remote station to onlycommunicate with single carrier base station's in a single carrierprotocol should be used when a remote station travels from a mixedcoverage area to a single carrier coverage area, such as at point 550.Example 4, below, speaks to this.

FIG. 21 is a flowchart of the methodology that can be used to implementeach of the handoff embodiments described above for a non-homogenousnetwork. In block 2110, each base station generates a list ofneighboring base stations using methods known to one skilled in the art.The process then proceeds to block 2120.

In block 2120, each base station transmits a neighbor list messagecontaining the list of neighboring base stations. The neighbor listmessage will indicate the pilot offsets of each of the neighboring basestations, and will either explicitly or implicitly indicate thefrequency at which each neighboring pilot signal is transmitted.Additionally, the neighbor list may state additional information abouteach neighboring base station, such as whether it is a single carrierbase station or a multi-carrier base station, or the frequency bands ituses for communication. Alternatively this additional information can betransmitted on another channel, such as a paging channel. The processthen proceeds to block 2130.

In block 2130, the remote station receives the neighbor list message andmonitors for pilots at frequencies and pilot offsets indicated by theneighbor list message. The remote station gathers signal strengthmeasurements of the pilots it is attempting to detect, and places thisinformation into a signal strength measurement message, which it thentransmits. In one embodiment the remote station only transmitsinformation in the signal strength measurement message for signals thatare received above a pre-determined threshold (such as pre-determinedEc/Io threshold, as would be known to one skilled in the art). A methodand apparatus for generating a signal strength measurement messagecontaining pilot strength information is disclosed in U.S. patentapplication Ser. No. 09/502,279, filed on Feb. 10, 2000, and entitled“METHOD AND APPARATUS FOR GENERATING PILOT STRENGTH MEASUREMENTMESSAGES”, assigned to the assignee of the present invention andincorporated in its entirety herein by reference. Other methods forgenerating signal strength measurement messages containing pilotstrength information are known to those skilled in the art. The processthen proceeds to block 2140.

In block 2140, the base station(s) receive the signal strengthmeasurement message. These base stations provide the signal strengthmeasurements to the BSC responsible for handoff. The process thenproceeds to block 2150.

In block 2150, the BSC examines the current state of communications withthe remote station along with the signal strength measurements receivedfrom the remote station, and uses these to determine the new Active Set,the set of base stations with which the remote station shouldcommunicate, and whether or not to initiate a handoff in accordance withone of the above-described embodiments. For example, if the currentstate of the remote station is such that it is only in communicationswith narrowband base stations, but the received signal strengthmeasurements indicate that the remote station is receiving strong pilotsignal measurements both from single carrier base stations and from amulti-carrier base station, then the BSC would initiate a handoff of theabove-described embodiments.

If the new active set contains only single carrier base stations, andthe remote station is only in communication with single carrier basestations at the present time and those communications utilize the singlecarrier protocol, then although a handoff will be performed, it will bea handoff other than that of the above-described embodiments. Likewise,if the new active set contains only multi-carrier base stations, and theremote station is only in communication with multi-carrier base stationsat the present time and those communications utilize the multi-carrierprotocol, then although a handoff will be performed, it will be ahandoff other than that of the above-described embodiments. In thesecases, the process proceeds to block 2110.

In all other cases, a handoff of the above-described embodiments will beperformed, and the process proceeds to block 2160. In block 2160, theBSC instructs at least one base station to transmit to the remotestation a handoff message containing instructions for the remote stationto perform a handoff. In one embodiment, all base stations that theremote station is currently communicating with transmit the remotestation a handoff message containing instructions for the remote stationto perform a handoff to the new active set). Depending on the radiopropagation environment of the remote station, and depending on whichparticular handoff embodiment of the above-described embodiments acarrier wishes to use, the handoff message will contain the appropriatesubset of handoff instructions as described in reference to theparticular handoff embodiment chosen (i.e., a given carrier can choosewhether to use any one of the first through the eighth handoffembodiments). Radio propagation environment is mentioned, because asmentioned in the descriptions of the various handoff embodiments, thehandoff performed is dependent upon the location of a remote station inrelation to the radio signals that it is able to receive from a set ofremote stations at any given time.

For instance, if a carrier wanted to support the eighth handoffembodiment, the handoff message transmitted in block 2160 would be basedupon the location of the remote station in accordance with thedescription of the eighth handoff embodiment. Below are examples showinghow the location affects the message transmitted in the eighth handoffembodiment.

EXAMPLE 1

remote station at point 520 (going from single carrier coverage intomixed coverage). If a remote station at point 520 transmitted a signalstrength measurement message in accordance with block 2130, then, inaccordance with the description of the eighth embodiment, a handoffmessage would be transmitted at block 2160 that instructs the remotestation to begin transmitting data in accordance with a single carrierprotocol in frequency band Nra (described in reference to the fourthhandoff embodiment), and to begin receiving data in accordance with amulti-carrier protocol in frequency band Wf from at least onemulti-carrier base station BS3. The handoff message also instructs theremote station to begin receiving data in accordance with amulti-carrier protocol in a single carrier frequency band Nf from atleast one single carrier base station BS1.

EXAMPLE 2

remote station at point 530 (going from mixed coverage intomulti-carrier coverage). If a remote station at point 530 transmitted asignal strength measurement message in accordance with block 2130, then,in accordance with the description of the eighth embodiment, a handoffmessage would be transmitted at block 2160 that instructs the remotestation to stop single carrier communications with a set of at least onemulti-carrier base stations BS3 and to begin multi-carriercommunications on the same set of base stations in frequency bands Wfand Wr.

EXAMPLE 3

the remote station at point 540 (going from multi-carrier coverage intomixed coverage). If a remote station at point 540 transmitted a signalstrength measurement message in accordance with block 2130, then, inaccordance with the description of the eighth embodiment, a handoffmessage would be transmitted at block 2160 that instructs the remotestation to begin transmitting data in accordance with a single carrierprotocol in frequency band Nra (described in reference to the fourthhandoff embodiment), and to begin receiving data in accordance with amulti-carrier protocol in frequency band Wf from at least onemulti-carrier base station BS3. The handoff message also instructs theremote station to begin receiving data in accordance with amulti-carrier protocol in Nf from at least one single carrier basestation BS1.

EXAMPLE 4

the remote station at point near point 550 (going from mixed coverageinto single carrier coverage). If a remote station at point 550transmitted a signal strength measurement message in accordance withblock 2130, then, in accordance with the description of the eighthembodiment, a handoff message would be transmitted at block 2160 thatinstructs the remote station to cease all communications usingmulti-carrier protocols, and to only communicate with a set of at leastone single carrier base stations BS1 using single carrier communicationsin frequency bands Nf and Nr.

Although these specific examples are related to the eighth handoffembodiment, after reading the description of all eight handoffembodiments described above one skilled in the art will recognize whathandoff messages will need to be transmitted in block 2160 based uponthe handoff embodiment chosen and the signal strength measurementsreceived from the remote station (these measurements allow the basestation controller to estimate the location of the remote station). Theprocess then proceeds to block 2170.

In block 2170, in accordance with the location of the remote station andin accordance with the particular handoff embodiment chosen, the basestation controller instructs the base stations to perform accordingly.These instructions will be consistent with the handoff messagetransmitted in block 2160. If in accordance with the particular handoffembodiment one or more base stations should cease or alter theircommunications with the remote station, they are instructed to do so.Likewise, if in accordance with the particular handoff embodiment one ormore base stations should begin communications with the remote station,they are instructed to do so in accordance with the handoff message ofblock 2160.

As an example, if a carrier wanted to support the eighth handoffembodiment, and the remote station was at point 520, and thus thehandoff message described in reference to Example 1 of block 2160 wastransmitted, then in block 2170 the base station controller wouldinstruct at least one multi-carrier base station BS3 to setup a forwardlink to the remote station for data transmissions in accordance with amulti-carrier protocol, and to setup a reverse link to the remotestation for receiving data transmissions in accordance with a singlecarrier protocol in a frequency band Nra (as described in reference tothe fourth handoff embodiment). Additionally, the base stationcontroller instructs at least one single carrier base station BS1 thatwas communicating in single carrier mode with the remote station priorto the handoff to stop receiving data from the remote station, and toalter the mode of transmission to the remote station to a mode in whichit transmits in a single carrier frequency band Nf a portion of a signalgenerated in accordance with a multi-carrier protocol.

Although this specific example is related to the eighth handoffembodiment in a scenario wherein the remote station moved from singlecarrier coverage to mixed coverage, after reading the description of alleight handoff embodiments described above one skilled in the art willrecognize what instructions the base station controller will give to thebase stations in block 2170 based upon the handoff embodiment chosen andthe estimated location of the remote station (as can be determined bythe signal strength measurements using procedures known to one skilledin the art). The process then proceeds to block 2180.

In block 2180, the remote station receives the handoff messagetransmitted in block 2160, and complies with the instructions. If thereceived handoff message either explicitly or implicitly instructs theremote station to cease receiving communications from one or more basestations, the remote station will stop receiving data communicationsfrom those base stations. Also, if the remote station is instructed tobegin listening to transmissions from one or more base stations, it willdo so.

If the handoff message instructs the remote station to switch its modeof reception from a single carrier mode to a multi-carrier mode, it willdo so. Conversely, if the handoff message instructs the remote stationto switch its mode of reception from a multi-carrier mode to a singlecarrier mode, it will do so.

If the handoff message instructs the remote station to switch its modeof transmission from a single carrier mode to a multi-carrier mode itwill do so. Conversely, if the handoff message instructs the remotestation to switch its mode of transmission from a multi-carrier mode toa single carrier mode it will do so. Additionally, if the handoffmessage instructs the remote station to transmit in data in a singlecarrier mode in a particular single carrier frequency band (e.g., Nrversus Nra in the first through eighth embodiments), the remote stationwill begin transmitting data in a single carrier mode in that particularsingle carrier frequency band.

As an example, if a carrier wanted to support the eighth handoffembodiment, and the remote station was at point 520, and thus thehandoff message described in reference to Example 1 of block 2160 wastransmitted, then in block 2180 the remote station would begintransmitting data on the reverse link in accordance with a singlecarrier protocol in a frequency band Nra (as described in reference tothe fourth handoff embodiment), and it would change its forward linkmode of reception to one in which it receives data in accordance with amulti-carrier protocol. In addition to receiving a multi-carriertransmission from at least one multi-carrier base station BS3, theremote station would begin receiving a portion of a signal generated inaccordance with the multi-carrier protocol that was transmitted over atleast one single carrier base station BS1. In one embodiment the remotestation is instructed to only decode the portion of the signal thatoccurs in the single carrier frequency band because the single carrierbase stations BS1 will only be transmitting a portion of themulti-carrier signal. In an alternative embodiment, the remote stationis simply instructed to decode the entire multi-carrier signal from thesingle carrier base stations BS1. In such an embodiment, although theremote station will not be able to decode the entire expectedmulti-carrier signal from BS1, but rather only the portion that wastransmitted by BS1, the absence of some of the signal will notnegatively impact the remote station when decoding the entiremulti-carrier signal as received from BS3.

Although this specific example is related to the eighth handoffembodiment in a scenario wherein the remote station moved from singlecarrier coverage to mixed coverage, after reading the description of alleight handoff embodiments described above one skilled in the art willrecognize what instructions the base station controller will put intothe handoff message in block 2160, based upon the handoff embodimentchosen and the estimated location of the remote station (as can bedetermined by the signal strength measurements using procedures known toone skilled in the art), and therefore will be able to determine whatthe remote station does in block 2180 in response to the reception ofthe handoff message. The process then proceeds to block 2110.

In FIG. 22, base station 2200 generates a neighbor list message inmessage generator 2220 and provides the message to modulator 2230. Themessage is modulated by modulator 2230 and provided to transmitter 2240,which upconverts and amplifies the signal and transmits the resultingsignal through antenna 2250.

In one embodiment, modulator 2230 is a multi-mode modulator, capable ofperforming modulation in compliance with a single carrier protocol andalso capable of performing modulation in compliance with a multi-carrierprotocol. In one such embodiment, modulator 2230 performs single carriermodulation in compliance with the 1X protocol and performs multi-carriermodulation in compliance with the 3X protocol. In an embodiment in whichmodulator 2230 is a multi-mode modulator, prior to performing modulationcontrol processor 2260 instructs modulator 2230 as to whether it shouldmodulate messages in accordance with a single carrier protocol or amulti-carrier protocol, as described in accordance with handoffembodiments 1 through 8. In one embodiment modulator 2230 is physicallycomprised of two separate modulators, one of which performs singlecarrier modulation, and another of which performs multi-carriermodulation. Control Processor 2260 either contains internal memory, orit is able to set and retrieve the value of memory in an external memoryunit (not shown), as is commonly known in the art.

In one embodiment, transmitter 2240 is a multi-mode transmitter, capableof transmitting in a multi-carrier frequency band, and also capable oftransmitting in a single carrier frequency band (such as 1.25 MHz for1X). In an embodiment in which transmitter 2240 is a multi-modetransmitter, prior to performing transmissions, control processor 2260instructs transmitter 2240 as to whether it should transmit messages ina single carrier frequency band or in a multi-carrier frequency band.

One skilled in the art will recognize that control processor 2260 may beimplemented using field-programmable gate arrays (FPGA), programmablelogic devices PLD), digital signal processors (DSP), one or moremicroprocessors, application specific integrated circuit (ASIC) or otherdevice capable of performing the functions described above.

Referring to FIG. 23, the transmitted signal is received by remotestation 2300 by antenna 2394, after which it passes through duplexer2392 to receiver 2390, which downconverts, filters and amplifies thesignal. Receiver 2390 is a multi-mode receiver capable of receiving datain a single carrier frequency band, and also capable of receiving datain a multi-carrier frequency band. Control processor 2320 instructsreceiver 2390 whether to be in single carrier or multi-carrier receiptmode any given moment, in accordance with handoff embodiments 1-8.Control Processor 2320 either contains internal memory, or it is able toset and retrieve the value of memory in an external memory unit (notshown), as is commonly known in the art.

The received signal is then demodulated by demodulator 2370 and providedto control processor 2320. Demodulator 2370 is a multi-mode demodulator,capable of performing demodulation in compliance with a single carrierprotocol and also capable of performing demodulation in compliance witha multi-carrier protocol. In one such embodiment, demodulator 2370performs single carrier demodulation in compliance with the 1X protocoland performs multi-carrier demodulation in compliance with the 3Xprotocol. Prior to performing demodulation, control processor 2320instructs demodulator 2370 as to whether it should modulate messages inaccordance with single carrier protocol 1X or multi-carrier protocol 3X,as described in accordance with handoff embodiments 1 through 8.

Demodulator 2370 provides the neighbor list message to Control processor2320, which then generates a set of commands directing a search to beperformed by searcher 2380. Searcher 2380 provides a set of searchdemodulation parameters to demodulator 2370. The demodulated signals areprovided to pilot energy accumulator 2330, which measures the strengthof the pilots of the base stations of the neighbor list. The energy ofeach of these neighbors is provided to control processor 2320, whichcompares the measured energy with a predetermined threshold T_ADD.Control processor 2320 generates a message that signifies which, if any,of the neighboring base station's signals exceeded the threshold T_ADD.Hereinafter, the term Active Set is used to identify these neighboringbase stations.

The message is provided to modulator 2350, where it is modulated. Themodulated signal is then provided to transmitter 2360, where it isupconverted and amplified, after which it travels through duplexer 2392to antenna 2394, where it is transmitted.

Modulator 2350 is a multi-mode modulator, capable of performingmodulation in compliance with a single carrier protocol and also capableof performing modulation in compliance with a multi-carrier protocol. Inone such embodiment, modulator 2350 performs single carrier modulationin compliance with the 1X protocol and performs multi-carrier modulationin compliance with the 3X protocol. In an embodiment in which modulator2350 is a multi-mode modulator, prior to performing modulation controlprocessor 2320 instructs modulator 2350 as to whether it should modulatemessages in accordance with a single carrier protocol or a multi-carrierprotocol, as described in accordance with handoff embodiments 1 through8. In one embodiment, transmitter 2360 is a multi-mode transmitter,capable of performing transmissions in a single carrier frequency band(such as 1.25 MHz for 1X) and in a multi-carrier frequency band (such asthree 1.25 MHz chunks for 3X). In such an embodiment, control processor2320 instructs transmitter 2360 whether to transmit in a single carrierfrequency band or in a multi-carrier frequency band. In an embodimentthat can be used to support the 4^(th) and 7^(th) handoff embodiments,wherein the remote station can transmits in one of two single carrierfrequencies (e.g. Nr or Nra) depending upon the coverage areas that itis in, control processor 2320 instructs transmitter 2360 as to whichfrequency band to transmit in.

Referring back to FIG. 22, the message indicating the strengths of theneighboring base stations is received by antenna 2290 of base station2200. The signal is downconverted and amplified by receiver 2280 andprovided to demodulator 2270. Demodulator 2270 demodulates the signaland provides the result to control processor 2260. Control processor2260 generates an Active Set list for the BSC in accordance with theinformation in the message transmitted by remote station 2300 indicatingthe results of its search. In the exemplary embodiment, the Active Setlist will consist of all base stations whose signals, when monitored byremote station 2300, exceeded the energy threshold T_ADD.

In one embodiment, receiver 2280 can receive data both in amulti-carrier frequency band and in a single carrier frequency band. Insuch an embodiment, control processor 2260 instructs receiver 2280whether to receive in a multi-carrier frequency band or in a singlecarrier frequency band. In an embodiment that can be used to support the4^(th) and 7^(th) handoff embodiments, wherein the base stationanticipates the remote station can transmitting in one of two singlecarrier frequencies (e.g. Nr or Nra), control processor 2260 instructsreceiver 2280 as to which frequency band to receive in.

Control Processor 2260 sends the Active Set list to interface 2210,which forwards a message indicating the Active Set list to the BSC.Interface 2210 can be any interface that allows for communicationbetween the base station and the BSC. In a centralized system, suchinterfaces are known in the art and include, but are not limited to,ethernet interfaces, T1 interfaces, E1 interfaces, ATM interfaces, andmicrowave interfaces. In a decentralized system, interface 2210 couldsimply be a memory bus or an area of shared memory. Capacity issuesallowing, the BSC provides forward link channels on a subset of basestations in the Active Set list. The forward link channels are setup oneach base station 2200 in accordance with the Active Set list, and inaccordance with the handoff embodiment being used. Additionally, reverselink channels are setup on each base 2200 in accordance with the ActiveSet list, and in accordance with the handoff embodiment being used. Asper the above-described handoff embodiments, it is possible that forwardlink channels can be setup on certain base stations without setting upreverse link channels on those base stations (e.g. the eighth handoffembodiment). Also, as per the above-described handoff embodiments, it ispossible that reverse link channels can be setup on certain basestations without setting up forward link channels on those base stations(e.g., the third and fourth handoff embodiments).

In one embodiment, control Processor 2260 also provides the Active Setlist to message generator 2220. The resulting handoff message ismodulated by modulator 2230 and transmitted as described above. In oneembodiment, the handoff message explicitly states which frequencies theremote station should begin receiving and transmitting on and whetherthe data should be modulated in a single carrier format (e.g. 1X) ormulti-carrier format (e.g., 3X). Such a handoff message is generated inaccordance with the handoff embodiment being used. In one embodiment,the handoff message merely states which base stations the remote stationis to communicate with, and the remote station is implicitly able totell which frequencies to communicate with from the receipt of othermessages detailing the capabilities of each base station.

In an alternative embodiment, a control processor 2420 of BSC 2400,diagrammed in FIG. 24, generates the handoff message in accordance withthe Active Set list and in accordance with the handoff embodiment beingused. In such an embodiment, control processor 2420 sends the generatedhandoff message to each base station 2200 with which the remote stationis currently communicating. Control processor 2420 sends the handoffmessage to base stations 2200 via BSC interface 2410. In such anembodiment, each control processor 2260 receives the handoff messagegenerated by the BSC via interface 2210. In such an embodiment, controlProcessor 2260 of base station 2200 provides the handoff message tomodulator 2230, which modulates the handoff message and transmits it asdescribed above.

Interface 2410 can be any interface that allows for communicationbetween the base station and the BSC. In a centralized system, suchinterfaces are known in the art and include, but are not limited to,ethernet interfaces, T1 interfaces, E1 interfaces, ATM interfaces, andmicrowave interfaces. In a decentralized system, interface 2410 couldsimply be a memory bus or an area of shared memory. Control Processor2420 either contains internal memory, or it is able to set and retrievethe value of memory in an external memory unit (not shown), as iscommonly known in the art. One skilled in the art will recognize thatcontrol processor 2420 may be implemented using field-programmable gatearrays (FPGA), programmable logic devices PLD), digital signalprocessors (DSP), one or more microprocessors, application specificintegrated circuit (ASIC) or other device capable of performing thefunctions described above.

Remote station 2300 receives the message by antenna 2394, demodulatesthe signal as described above, and provides the message to controlprocessor 2320. Control processor 2320 then provides informationregarding the Active Set list to demodulator 2370 and receiver 2390, anda handoff is attempted using the parameters of the base stations in theActive Set list. It should be noted that because, in this example, theActive Set is based upon previous information generated by remotestation 2300, the remote station 2300 need not receive the Active Setlist, because it often knows the stations on the list a priori. Thus, inan alternative embodiment, the remote station may delay a predeterminedtime period and perform handoff to the base stations whose signalexceeded the threshold. If, on the other hand, the active set is notsimply a copy of the base stations which exceeded the threshold, butrather also takes into account parameters unknown to the remote station,such as capacity parameters of other base stations, then transmission ofthe message would prove of value.

One skilled in the art will recognize that control processor 2320 may beimplemented using field-programmable gate arrays (FPGA), programmablelogic devices PLD), digital signal processors (DSP), one or moremicroprocessors, application specific integrated circuit (ASIC) or otherdevice capable of performing the functions described above.

The previous description of the embodiments is provided to enable aperson skilled in the art to make or use the present invention. Thevarious modifications to these embodiments will be readily apparent tothose skilled in the art, and the generic principles defined herein maybe applied to other embodiments without the use of the inventivefaculty. Additionally, the various methods taught herein can be combinedwith each other in any manner without the use of the inventive faculty.Thus, the present invention is not intended to be limited to theembodiments shown herein but is to be accorded the widest scopeconsistent with the principles and novel features disclosed.

1. A method of facilitating a remote station hand-off, comprising: receiving signals in a first frequency band in accordance with a single carrier protocol at said remote station; transmitting signal strength measurements of various base stations in a first message from said remote station, wherein the various base stations are a subset of base stations in a neighbor list message received by the remote station; and receiving a second message at said remote station that indicates that said remote station should begin receiving signals in accordance with a multi-carrier protocol in a second frequency band.
 2. The method of claim 1 wherein said first frequency band is contained within said second frequency band.
 3. The method of claim 1 wherein said second message also indicates that said remote station should begin transmitting messages in accordance with said multi-carrier protocol on a second frequency band that is larger than said first frequency band.
 4. The method of claim 1 further comprising: receiving at said remote station from said at least one of various base stations that is multi-carrier compliant, signals in accordance with said single carrier protocol in said first frequency band; and monitoring, from said at least one of said various base stations that is multi-carrier compliant, a second frequency band for signals transmitted in accordance with said single carrier protocol in said second frequency band.
 5. A remote station, comprising: means for receiving signals in a first frequency band in accordance with a single carrier protocol; means for transmitting signal strength measurements of various base stations in a first message, wherein the various base stations are a subset of base stations in a neighbor list message received by the remote station; and means for receiving a second message that indicates that said remote station should begin receiving signals in accordance with a multi-carrier protocol in a second frequency.
 6. The remote station of claim 5, wherein said first frequency band is contained within said second frequency band.
 7. The remote station of claim 5 wherein said second message also indicates that said remote station should begin transmitting messages in accordance with said multi-carrier protocol on a second frequency band that is larger than said first frequency band.
 8. The remote station of claim 5 further comprising: means for receiving at said remote station from said at least one of various base stations that is multi-carrier compliant, signals in accordance with said single carrier protocol in said first frequency band; and means for monitoring, from said at least one of said various base stations that is multi-carrier compliant, a second frequency band for signals transmitted in accordance with said single carrier protocol in said second frequency band.
 9. A computer readable media embodying a method comprising of facilitating a remote station hand-off, the method comprising: receiving signals in a first frequency band in accordance with a single carrier protocol at said remote station; transmitting signal strength measurements of various base stations in a first message from said remote station, wherein the various base stations are a subset of base stations in a neighbor list message received by the remote station; and receiving a second message at said remote station that indicates that said remote station should begin receiving signals in accordance with a multi-carrier protocol in a second frequency band.
 10. A computer readable media embodying a method comprising of facilitating a remote station hand-off, the method comprising: receiving signals in a first frequency band in accordance with a single carrier protocol at said remote station; transmitting signal strength measurements of various base stations in a first message from said remote station, wherein the various base stations are a subset of base stations in a neighbor list message received by the remote station; and receiving a second message at said remote station that indicates that said remote station should begin receiving messages in accordance with a multi-carrier protocol in a second frequency band that is larger than said first frequency band, and wherein said second message also indicates that said remote station should begin transmitting messages in accordance with said multi-carrier protocol on a second frequency band that is larger than said first frequency band, and further, wherein the second message is responsive to a determination that at least one of various base stations is single-carrier compliant and at least one of various base stations is multi-carrier compliant.
 11. A computer readable media of claim 10, wherein the method embodied further comprises: receiving at said remote station from said at least one of various base stations that is multi-carrier compliant, signals in accordance with said single carrier protocol in said first frequency band; and monitoring, from said at least one of said various base stations that is multi-carrier compliant, a second frequency band for signals transmitted in accordance with said single carrier protocol in said second frequency band. 